Allow users to appear anonymously while spectating games

[srstinson]

Loads the value created in lichess-org/lila#14775 from MongoDB and modifies the table of spectators to store whether that user appears anonymously or not.

Then, when reporting the room status, will add users appearing anonymously to the anon count and remove them from the list of users specified.

User spectating a game anonymously using this setting:

The only thing I was not sure about was whether or not to look up the user's preference in MongoDB or have it be sent as part of the call to the websocket. I chose to do the lookup here to decouple the logic more but I can see the extra db call being something we would want to avoid. Another option would be to not care about the user's preference all all while connecting but to handle it when the room's status is requested, but I felt that would lead to an extremely large number of db calls.

[ornicar]

Thanks, but I don't agree that the feature is worth the extra code and the performance penalty of adding one database request every time someone watches a game.