`CODER_MOUNTS` and `/envbox docker --mounts` CernVM-FS issue

I am running coder on a k8s cluster. My outer container is the a modified envbox docker image that has cvmfs installed (without installing it mounting doesn't work). My inner container is an Ubuntu 20:04 image with cvmfs installed as well (just to be safe).

My outer container has cvmfs mount with a HostToContainer mount propagation. However, whether through `CODER_MOUNTS` or `/envbox docker --mounts`, I face issues mounting my cvmfs from the outer to the inner container.

The command:
```
/envbox docker --mounts /tools/Xilinx:/tools/Xilinx:ro
```

The output (trimmed):
```
{"output":"Failed to run envbox: remount: mount failed: exit status 2\nMounting command: mount\nMounting arguments: -o remount,rw /tools/Xilinx\nOutput: The CernVM File System\nVersion 2.11.0\nCopyright (c) 2009- CERN, all rights reserved\n\nPlease visit http://cernvm.cern.ch for details.\n\nUsage: cvmfs2 [-h] [-V] [-s] [-f] [-d] [-k] [-o mount options] \u003crepository name\u003e \u003cmount point\u003e\n\nCernVM-FS general options:\n --help|-h Print Help output (this)\n --version|-V Print CernVM-FS version\n -s Run singlethreaded\n -f Run in foreground\n -d Enable debugging\n -k Parse options\nCernVM-FS mount options:\n -o config=FILES colon-separated path list of config files\n -o uid=UID Drop credentials to another user\n -o gid=GID Drop credentials to another group\n -o system_mount Indicate that mount is system-wide\n -o grab_mountpoint give ownership of the mountpoint to the user before mounting (required for autofs)\n -o parse Parse and print cvmfs parameters\n -o cvmfs_suid Enable suid mode\n\n -o disable_watchdog Do not spawn a post mortem crash handler\n -o foreground Run in foreground\n -o libfuse=[2,3] Enforce a certain libfuse version\nFuse mount options:\n -o allow_other allow access to other users\n -o allow_root allow access to root\n -o nonempty allow mounts over non-empty directory\n\n","time":"2023-10-14T12:44:13.421245546-07:00","type":"error"}
{"output":"Failed to run envbox: run: remount: mount failed: exit status 2\nMounting command: mount\nMounting arguments: -o remount,rw /tools/Xilinx\nOutput: The CernVM File System\nVersion 2.11.0\nCopyright (c) 2009- CERN, all rights reserved\n\nPlease visit http://cernvm.cern.ch for details.\n\nUsage: cvmfs2 [-h] [-V] [-s] [-f] [-d] [-k] [-o mount options] \u003crepository name\u003e \u003cmount point\u003e\n\nCernVM-FS general options:\n --help|-h Print Help output (this)\n --version|-V Print CernVM-FS version\n -s Run singlethreaded\n -f Run in foreground\n -d Enable debugging\n -k Parse options\nCernVM-FS mount options:\n -o config=FILES colon-separated path list of config files\n -o uid=UID Drop credentials to another user\n -o gid=GID Drop credentials to another group\n -o system_mount Indicate that mount is system-wide\n -o grab_mountpoint give ownership of the mountpoint to the user before mounting (required for autofs)\n -o parse Parse and print cvmfs parameters\n -o cvmfs_suid Enable suid mode\n\n -o disable_watchdog Do not spawn a post mortem crash handler\n -o foreground Run in foreground\n -o libfuse=[2,3] Enforce a certain libfuse version\nFuse mount options:\n -o allow_other allow access to other users\n -o allow_root allow access to root\n -o nonempty allow mounts over non-empty directory\n\n","time":"2023-10-14T12:44:13.421327848-07:00","type":"error"}
{"output":"","time":"2023-10-14T12:44:13.421404419-07:00","type":"done"}
{"ts":"2023-10-14T19:44:13.421414299Z","level":"ERROR","msg":"send startup logs","caller":"/home/runner/work/envbox/envbox/buildlog/coder.go:116","func":"github.com/coder/envbox/buildlog.(*CoderLogger).processLogs.func1","fields":{"error":"Patch \"https://coder.nrp-nautilus.io/api/v2/workspaceagents/me/startup-logs\": context canceled"}}
run: remount: mount failed: exit status 2
Mounting command: mount
Mounting arguments: -o remount,rw /tools/Xilinx
Output: The CernVM File System
Version 2.11.0
Copyright (c) 2009- CERN, all rights reserved

Please visit http://cernvm.cern.ch for details.

Usage: cvmfs2 [-h] [-V] [-s] [-f] [-d] [-k] [-o mount options]

CernVM-FS general options:
--help|-h Print Help output (this)
--version|-V Print CernVM-FS version
-s Run singlethreaded
-f Run in foreground
-d Enable debugging
-k Parse options
CernVM-FS mount options:
-o config=FILES colon-separated path list of config files
-o uid=UID Drop credentials to another user
-o gid=GID Drop credentials to another group
-o system_mount Indicate that mount is system-wide
-o grab_mountpoint give ownership of the mountpoint to the user before mounting (required for autofs)
-o parse Parse and print cvmfs parameters
-o cvmfs_suid Enable suid mode

-o disable_watchdog Do not spawn a post mortem crash handler
-o foreground Run in foreground
-o libfuse=[2,3] Enforce a certain libfuse version
Fuse mount options:
-o allow_other allow access to other users
-o allow_root allow access to root
-o nonempty allow mounts over non-empty directory
```

I also tried mounting without installing cvmfs. That also fails on command cvmfs2 is not installed.

Start by reproducing the `/envbox docker --mounts /tools/Xilinx:/tools/Xilinx:ro` command and compare it with the `CODER_MOUNTS` path. The reported startup failure points to `buildlog/coder.go:116`, while the mount behavior is exposed through the `/envbox docker` entry point. Done means the reported CernVM-FS mount no longer fails with the remount error.

索引モデルが issue の本文から書いたものです。