create: add an --add-parents option?

## Have you checked borgbackup docs, FAQ, and open Github issues?

Yes

## Is this a BUG / ISSUE report or a QUESTION?

Question, maybe a bug

## System information. For client/server mode post info for both machines.

#### Your borg version (borg -V).
1.1.15

#### Operating system (distribution) and version.
Fedora 32

#### Hardware / network configuration, and filesystems used.
No network, local filesystem only: btrfs, fuse, tmpfs

#### How much data is handled by borg?
~1GB

#### Full borg commandline that lead to the problem (leave away excludes and passwords)

Let's check ownership and file permissions of home directories:
```
ls -l /home/
drwx------. 62 user1 user1 4096 9. Feb 21:15 user1
drwx------. 16 user2 user2 4096 8. Feb 22:19 user2
```

As root:
Create a repository and backup /home/user2 and /home/user1/subdir
```
borg init --encryption=repokey-blake2 --storage-quota=10G --make-parent-dirs /tmp/borgtest/{hostname}
borg create --progress --stats /tmp/borgtest/{hostname}::{now} /home/user1/subdir /home/user2
```

Mount the backup to allow users to restore their own files:
```
mkdir /tmp/borgtest/mount
borg mount -o allow_other /tmp/borgtest/{hostname} /tmp/borgtest/mount
chmod 755 /tmp/borgtest
```

As user1:
```
cd /tmp/borgtest/mount/2021-02-09T20:46:05/home
ls -l
drwxr-xr-x. 1 root root 0 9. Feb 20:47 user1
drwx------. 1 user2 user2 0 8. Feb 22:19 user2
```
Homedirectory of user1 is owned by root and permissions are set to 755!?

As root again:
Let's check what borg extract does, to see if this behaviour is fuse specific:
```
borg umount /tmp/borgtest/mount
mkdir /tmp/borgtest/restore
cd /tmp/borgtest/restore/
borg extract --progress --strip-components=1 /tmp/borgtest/{hostname}::2021-02-09T20:46:05
ls -l
drwx------. 3 root root 60 9. Feb 20:51 user1
drwx------. 16 user2 user2 600 8. Feb 22:19 user2
```
Ownership is still root/root, but permissions looks okay. So this differs from source and borg mount.

## Describe the problem you're observing.
Directory ownership differs from source if only a subdirectory is backed up.
Directory ownership and permissions differs from source if only a subdirectory is backed up and repository is mounted with fuse.

Questions is: Did I made a mistake? Is this behaviour intended and I missed something in the documentation? Or did I found a bug?

#### Can you reproduce the problem? If so, describe how. If not, describe troubleshooting steps you took before opening the issue.
Yes, I can reproduce this as described. The above is a real world example, only user and directory names have been replaced for privacy .
I double checked with other homedirs and subdirectories and still had the same behaviour when mounting with fuse.

#### Include any warning/errors/backtraces from the system logs
None on stdout, dmesg or journalctl