feat: add occupied slots to game rooms api

[reinaldooli]

This is part of the changes to allow Maestro calculations to be based on the number of matches running in a Game Server. These changes will allow maestro to receive the number of running matches in a Game Server.

Changes

• Add running_matches param to the service definition files (proto)
• Create/Update Room Storage with the number of running matches. Later we'll be able to aggregate the values in this storage to know the total amount of running matches by scheduler.