Motivation is that to allow new players to join existing matches easily.
Idea 1: It would be nice to retrieve the currently active Matches from the Matchmaking v2 API for clients, with a ListCurrentMatches or similar API call.
Alternative idea: to make server backfilling a setting for the queue (exposed on UI / API), that would allow automatic backfilling if enabled, without the hassle to create server backfill tickets etc.
