Allow setting membership events visibility per room

[crater2150]

Describe the problem

In large public rooms, membership events can create a lot of noise, in some cases there are more of them than regular messages. On the other hand, I don't want to hide them completely, as they are relevant information in private rooms.

Describe the solution you'd like

Ideally, I'd like to be able to set the "Hide membership events" option on a per-room basis.

Alternatives considered

A maybe simpler alternative would be to add a third state to the "Hide membership events" setting: "Only in public rooms". I don't know if this would be easier to implement.

Additional context

No response