Join multiple teams

[ximk]

This would mainly be to give coaches the ability to appear on the team page of the team(s) they are coaching on top of the team they are already playing for (if they are on a team), but could also be applicable to players who are on two teams at once (maybe one for competitive and one for their collegiate team).

Squishy in the Discord said they'd be willing to work on it if this sounds like a good idea.