Extend RegisterGame & Matchmaking with user data field

As detailed in this thread

https://community.playfab.com/questions/16141/playfabserverapiregistergame-serverhost.html

I would like to request a simple extension for RegisterGameRequest(and the relevant return values for match making), so that non IP/Port based server platforms can have a mechanism to register a server using a string field based on the needs of the platform. For example, in Photons case, we'd need to register game servers by a room guid, and return them via match making calls so they can be joined properly