Disallow changing of the Gitlab username

See merge request archlinux/infrastructure!328

As keycloak is the canonical source of truth and interacting with gitlab
usually requires the username as identifier. As we don't want to
accidently assign permissions to a changed username disallow changing of
usernames altogether in Gitlab.

For symmetry with synapse-worker@.service.

To prevent mjolnir from failing.

Borg backup check

See merge request archlinux/infrastructure!322

Now that our textcollector depends on the condition of /backup being
available, we should be extra careful that we get rid of the directory.
If anything in the script fails, a trap now umounts and removes the
directory automatically if on btrfs.being available, we should be extra
careful that we get rid of the directory. If anything in the script
fails, a trap now umounts and removes the directory automatically if on
btrfs.

Currently our textcollector can sometimes fail with 'Failed to
create/acquire the lock /home/backup/$server/lock.exclusive (timeout)."
Instead of checking on a borg lock file, check if our backup snapshot
dir exists which the backup script creates and removes. This should give
less false positives then our current method.

Rate limit our archweb RSS feeds

See merge request archlinux/infrastructure!319

Cache urls which urls marks as can be cached by nginx. This offloads our
uwsgi workers and allows for speedier delivery of RSS feeds and other
cached routes.

Due to users misconfiguring their conky to query for rss updates every
second add proper rate limitting to all rss endpoints in nginx.

The websocket support always 400'd as upgrade headers where missing for
/socket.io

arch_boxes_sync: Override the "latest" link instead of following it

See merge request archlinux/infrastructure!318

Configure network correctly for Kape servers

See merge request archlinux/infrastructure!320

Previously we configured our network conf to all interfaces, which
shouldn't be done as not all our routed to the internet and this causes
systemd-network-online target to fail.