Feature request: Support not having root access to Nextcloud data folder

Description

In an unprivileged Proxmox lxc install if the data folder is an NFS mounted on the proxmox host and passed to the lxc container as a mount bind the root of the lxc won't have root privileges over the files within the mount. This causes the update script to fail even if www-data is owner of the data folder. Root squashing won't resolve the issue either with the current update script since some operations require root privileges over the files.

It should be fairly straightforward to modify the update script to detect not having root privileges on the mount on the fly and fall back to doing any file manipulations using www-data as the user.

I may look into this if I have time but no promises.

Start by locating the update script and reviewing the operations that require root privileges on the mounted data folder. Reproduce the unprivileged Proxmox LXC/NFS bind-mount case, then verify that the update completes by using www-data for file manipulations when root access is unavailable.