Player join to game: new API call: POST /game/{game_pk}/join/

[Virako]

POST /game/{game_pk}/join/

Player join to Game: this call should add Player to Content in a give position.
Player will be the player that realize call.

data = {
            'position': {
                'longitude': 37.201421,
                'latitude': -6.9447224
            }
}

return:

201 if Player is added to contents
401 if unauthorizhed
400 if data is incorrect
404 if game not exist