Rating service also creates default ratings

[Askaholic]

We want 2v2 rating to be initialized from global rating. This happens here for the purposes of matchmaking:

server/server/rating.py

Line 39 in 9e3d47e

if key == "tmm_2v2" and key not in self:

However, it seems that when games get rated, the default rating is created by the rating service, which doesn't have any logic for using a different rating as a base:

server/server/rating_service/rating_service.py

Line 227 in 9e3d47e

async def _create_default_rating(

It would be ideal if we could refactor the duplication of rating initialization so we don't have to have 2 implementations. We also need unit tests that check the values written to the database after a game.