upgrade or rebuild hetzner-hel1-01 (nagios/icinga)
Nagios is going to be a particularly tricky bullseye upgrade, so it's not part of the large bullseye upgrade batches (#40690 (closed) or #40692 (closed)).
We need to decide whether we keep icinga around at all or replace it with Prometheus (#29864 (closed)). if we do keep icinga, we need to decide whether we keep the current "push to git to rebuild the config" model or "puppetize the setup" (#32901).