feat(mastodon): Rework redis integration and add PodDisruptionBudgets

This patch adds PDBs for all main deployments with a hardcoded
maxUnavailable 1. This should help to make sure that updates go smooth
and without major downtimes, as soon as at least 2 replicas are running,
while still not blocking cluster updates.

Furhter it makes the redis dependency optional, helping to replace the
integrated redis with a separate or external redis service.