Allow room ignoring

Ignoring a room would imply ignoring any invitations to that room, and possibly not seeing that room when exploring. The room can be a pattern - any room matching the pattern would be ignored. The pattern could match the room title, names/aliases, subtext, or maybe even presence of a certain user.
Some use cases:
(1) Getting invited by someone who keeps making new accounts to do so.
(2) Ignoring a class of rooms - e.g. violence, sex, hate, occultism, .. -, or rooms that have aliases on certain servers.
(3) Avoiding a user.

The issue names no files, tests, or entry points. Start by clarifying the intended matching rules and which Element clients and room surfaces should honor them. Done would require an agreed scope for ignored invitations, room exploration, and pattern matching.

Written by the indexing model from the issue text.