poolcounter hosts are still buster, this is a tracking task for upgrading to bullseye
Notes:
- Poolcounter is now upstreamed in bullseye, it's no longer needed to package it.
- poolcounter-prometheus-exporter will need to be packaged for bullseye
- MediaWiki does the right thing when a poolcounter is unresponsive now, but it's best to deploy a mediawiki-config change (see 0e9520b5d as an example)
- Important: The upgrades must happen 1 by 1, otherwise we risk a really big outage.