nixos/nextcloud: set up base directories & override.config.php with tmpfiles

Closes #169733

The issue is that Nextcloud fails to start up after a GC because the
symlink from `override.config.php` is stale.

I'm relatively certain that this is not a bug in the Nix GC - that
would've popped up somewhere else already in the past years - and one of
the reporters seems to confirm that: when they restarted
`nextcloud-setup.service` after the issue appeared, an
`override.config.php` pointing to a different hash was there.

This hints that on a deploy `nextcloud-setup` wasn't restarted properly
and thus replacing the symlink update was missed. This is relatively
hard to trigger due to the nature of the bug unfortunately (you usually
keep system generations for a few weeks and you'll need to change the
configuration - or stdenv - to get a different `override.config.php`),
so getting pointers from folks who are affected is rather complicated.

So I decided to work around this by using systemd-tmpfiles which a lot
of other modules already utilize for this use-case. Now,
`override.config.php` and the directory structure aren't created by
`nextcloud-setup`, but by `systemd-tmpfiles`.

With that, the structure is guaranteed to exist

* on boot, since tmpfiles are always created/applied then
* on config activation, since this is done before services are
  (re)started which covers the case for new installations and existing
  ones.

Also, the recursive `chgrp` was used as transition tool when we switched
from `nginx` as owning group to a dedicated `nextcloud` group[1][2], but
this was several releases ago, so I don't consider this relevant
anymore.

[1] fd9eb16b249aad1d5e231b8329035abfab5fc0eb
[2] ca916e8cb3220ba43a43d10f72ccb4b88077a461

0 files changed, 0 insertions, 0 deletions