Adds a group of players to a game session. Similar to CreatePlayerSession, this action allows you to add multiple players in a single call, which is useful for games that provide party and/or matchmaking features. A game session must be in an ACTIVE status, have a creation policy of ALLOW_ALL, and have an open player slot before players can be added to the session.
To create player sessions, specify a game session ID and a list of player IDs. If successful, the players are added to the game session and a set of new PlayerSession objects is returned.