noempty should upload existing files to bucket?

**Describe the issue**
I expected that mounting gcsfuse on a directory with existing files would result in those files being synced to GCS. However, the files are not present in the dir when gcsfuse is started (my bucket is empty).

**To Collect more Debug logs**
Steps to reproduce the behavior:
1. Please make sure you have no other security, monitoring, background processes which can offend the FUSE process running. Possibly reproduce under a fresh/clean installation.
2. Please rerun with --debug_fuse --debug_fs --debug_gcs --debug_http --foreground as additional flags to enable debug logs.
3. Monitor the logs and please capture screenshots or copy the relevant logs to a file (can use --log-format and --log-file as well).
4. Attach the screenshot or the logs file to the bug report here.
5. If you're using gcsfuse with any other library/tool/process please list out the steps you took to reproduce the issue.

```
~/mount-folder$ echo "hello" > foo.txt

$ gcsfuse -o rw,nonempty --debug_fuse --debug_fs --debug_gcs --debug_http --foreground --implicit-dirs $BUCKET ~/mount-folder/
```

A few seconds later, the file is "deleted" (`ls` doesn't show it if gcsfuse is running, but it does if gcsfuse is stopped).

Logs:

```
{"name":"root","levelname":"INFO","severity":"INFO","message":"Start gcsfuse/1.0.1 (Go version go1.20.5) for app \"\" using mount point: /home/user/mount-folder/\n","timestampSeconds":1692055966,"timestampNanos":540149851}
{"name":"root","levelname":"INFO","severity":"INFO","message":"Opening GCS connection...\n","timestampSeconds":1692055966,"timestampNanos":540225421}
{"name":"root","levelname":"INFO","severity":"INFO","message":"Creating a mount at \"/home/user/mount-folder/\"\n","timestampSeconds":1692055966,"timestampNanos":543620609}
{"name":"root","levelname":"INFO","severity":"INFO","message":"Creating a new server...\n","timestampSeconds":1692055966,"timestampNanos":543676400}
{"name":"root","levelname":"INFO","severity":"INFO","message":"Set up root directory for bucket $BUCKET\n","timestampSeconds":1692055966,"timestampNanos":543692277}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x0: \u003c- ListObjects(\"\")\n","timestampSeconds":1692055966,"timestampNanos":543706580}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x0: -\u003e ListObjects(\"\") (164.540755ms): OK\n","timestampSeconds":1692055966,"timestampNanos":708261265}
{"name":"root","levelname":"INFO","severity":"INFO","message":"Mounting file system \"$BUCKET\"...\n","timestampSeconds":1692055966,"timestampNanos":708410485}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Beginning the mounting kickoff process\n","timestampSeconds":1692055966,"timestampNanos":708494846}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Parsing fuse file descriptor\n","timestampSeconds":1692055966,"timestampNanos":708536589}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Preparing for direct mounting\n","timestampSeconds":1692055966,"timestampNanos":708543068}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Successfully opened the /dev/fuse in blocking mode\n","timestampSeconds":1692055966,"timestampNanos":708572955}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Starting the unix mounting\n","timestampSeconds":1692055966,"timestampNanos":708609568}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Directmount failed. Trying fallback.\n","timestampSeconds":1692055966,"timestampNanos":708627188}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Creating a socket pair\n","timestampSeconds":1692055966,"timestampNanos":708695464}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Creating files to wrap the sockets\n","timestampSeconds":1692055966,"timestampNanos":708727252}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Starting fusermount/os mount\n","timestampSeconds":1692055966,"timestampNanos":708742879}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Wrapping socket pair in a connection\n","timestampSeconds":1692055966,"timestampNanos":710532113}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Checking that we have a unix domain socket\n","timestampSeconds":1692055966,"timestampNanos":710592272}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Read a message from socket\n","timestampSeconds":1692055966,"timestampNanos":710604488}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Successfully read the socket message.\n","timestampSeconds":1692055966,"timestampNanos":710618163}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Converting FD into os.File\n","timestampSeconds":1692055966,"timestampNanos":710628138}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Completed the mounting kickoff process\n","timestampSeconds":1692055966,"timestampNanos":710660210}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Creating a connection object\n","timestampSeconds":1692055966,"timestampNanos":710673050}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000002 connection.go:416] \u003c- init\n","timestampSeconds":1692055966,"timestampNanos":710996856}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000002 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055966,"timestampNanos":711032812}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Successfully created the connection\n","timestampSeconds":1692055966,"timestampNanos":711051389}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Waiting for mounting process to complete\n","timestampSeconds":1692055966,"timestampNanos":711066841}
{"name":"root","levelname":"INFO","severity":"INFO","message":"File system has been successfully mounted.\n","timestampSeconds":1692055966,"timestampNanos":711083128}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000004 connection.go:416] \u003c- GetInodeAttributes (inode 1, PID 1762)\n","timestampSeconds":1692055973,"timestampNanos":500172064}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000004 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055973,"timestampNanos":500480409}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000006 connection.go:416] \u003c- GetXattr (inode 1, name \"security.selinux\", PID 27132, name security.selinux)\n","timestampSeconds":1692055973,"timestampNanos":782008471}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000006 connection.go:500] -\u003e Error: \"function not implemented\"\n","timestampSeconds":1692055973,"timestampNanos":782166805}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000008 connection.go:416] \u003c- OpenDir (inode 1, PID 27132)\n","timestampSeconds":1692055973,"timestampNanos":782590176}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000008 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055973,"timestampNanos":782714333}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000a connection.go:416] \u003c- ReadDir (inode 1, PID 27132)\n","timestampSeconds":1692055973,"timestampNanos":782837321}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x1: \u003c- ListObjects(\"\")\n","timestampSeconds":1692055973,"timestampNanos":782914515}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x1: -\u003e ListObjects(\"\") (34.895007ms): OK\n","timestampSeconds":1692055973,"timestampNanos":817814151}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000a connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055973,"timestampNanos":817888715}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000c connection.go:416] \u003c- ReleaseDirHandle (PID 0)\n","timestampSeconds":1692055973,"timestampNanos":818017487}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000c connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055973,"timestampNanos":818134495}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000e connection.go:416] \u003c- OpenDir (inode 1, PID 27135)\n","timestampSeconds":1692055974,"timestampNanos":822768898}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x0000000e connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055974,"timestampNanos":823035572}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000010 connection.go:416] \u003c- GetInodeAttributes (inode 1, PID 27135)\n","timestampSeconds":1692055974,"timestampNanos":823130135}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000010 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055974,"timestampNanos":823274480}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000012 connection.go:416] \u003c- ReadDir (inode 1, PID 27135)\n","timestampSeconds":1692055974,"timestampNanos":823364910}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x2: \u003c- ListObjects(\"\")\n","timestampSeconds":1692055974,"timestampNanos":823424255}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"gcs: Req 0x2: -\u003e ListObjects(\"\") (43.3444ms): OK\n","timestampSeconds":1692055974,"timestampNanos":866772673}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000012 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055974,"timestampNanos":866882564}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000014 connection.go:416] \u003c- ReleaseDirHandle (PID 0)\n","timestampSeconds":1692055974,"timestampNanos":866983891}
{"name":"root","levelname":"DEBUG","severity":"DEBUG","message":"fuse_debug: Op 0x00000014 connection.go:498] -\u003e OK ()\n","timestampSeconds":1692055974,"timestampNanos":867057195}
```

**System (please complete the following information):**
- OS: 22.04.1-Ubuntu
- Platform: GCE VM
- Version: gcsfuse version 1.0.1

**Additional context**
Add any other context about the problem here.

**SLO:**
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