Turn off pings from outside teams

Currently, lichess sends a notification to users whenever that user is tagged in a post. This includes team posts, even when the user is not a member of the team and the team forums are closed to non-members.

It doesn't make sense to notify a user that they were mentioned if they are unable to see the post they were mentioned in.

It should also be mentioned that the option to unsubscribe only appears when you have access to the forum (so there is no way to "turn off" the pings).

Bump