* Alerting: Persist silence state immediately on Create/Delete
Persists the silence state to the kvstore immediately instead of waiting for the
next maintenance run. This is used after Create/Delete to prevent silences from
being lost when a new Alertmanager is started before the state has persisted.
This can happen, for example, in a rolling deployment scenario.
* Fix test that requires real data
* Don't error if silence state persist fails, maintenance will correct