Update a user's play count for a game

[RyanFrantz]

As a user, I want to be able to record the number of times I played a particular game.

Acceptance Criteria:

• Get current game counts for a user curl localhost:8080/user/1/games
• Update the count for one of the games: curl -X POST localhost:8080/user/1/games/train-of-thought (see 2nd implementation note)
• See that the play count has increased by 1 curl localhost:8080/user/1/games

Implementation Notes:

• Should have basic validation (e.g. the given game slug exists, etc)
• The final route and payload to POST to is up to the implementer (and we will update the Acceptance Criteria to match)
• Authentication is not in-scope for this story