Improve watchCommunitiesToUnmute

[osmaczko]

Problem

watchCommunitiesToUnmute reads all community info from the database in the loop. That's pretty expensive, see: #5012 (comment). Even though the problem was mitigated by increasing the interval, the procedure should be improved. Instead of unmarshaling all community data, only muted and mutedTill columns should be read from the db.

Acceptance Criteria

• CheckCommunitiesToUnmute quires only subset (muted&mutedTill) of community data

[jrainville]

One additional improvement that might be possible is to do the procedure only when there are muted communities. Right now, if there are no muted communities or if they are muted "indefinitely", we still run the procedure.

But that is a bit more error prone, since we need to start/restart the procedure once one community is muted with a timer, so it might not be worth it.