Endpoint to start games from a lobby

[CrsiX]

Require an endpoint to start a game from the lobby, e.g. POST /api/v2/lobby/startGame for the creator/owner of the lobby only. It should also trigger WebSocket notifications to all connected users in the specified lobby, so that they know the game has started. I wouldn't use UpdateGameData, but a similar struct which also includes the lobby ID that just got closed.

The owner will generate the initial map on its client and upload it along this request, i.e. startGame needs to accept the lobby as well as the initial game data. Afterwards, the game endpoints may be used on that game as well.