Add multi-game support for user intake

[gankoji]

• Refactor player service (particularly the create MLE player function for default args)
• Add new mutation in user resolver, which:
  • Registers a user and UAA
  • Creates a member within MLE
  • Loops over the input list of tuples of (skill_group, salary) to create a player for each corresponding game
  • Creates a single MLE player with the last salary and player ID from that loop