PlayerTracking: Be able to set GameServer capacity on Allocation

[markmandel]

Is your feature request related to a problem? Please describe.

When creating a GameServerAllocation, it would be useful to specify what the player tracking capacity is going to be on the allocated GameServer

Describe the solution you'd like

Draft of what the GameServerAllocation structure could look like (:

apiVersion: "allocation.agones.dev/v1"
kind: GameServerAllocation
spec:
  selectors:
    - matchLabels:
        agones.dev/fleet: lobby
      gameServerState: Allocated
      players:
        minAvailable: 10
        maxAvailable: 15
    - matchLabels:
        agones.dev/fleet: lobby
  players: # this is a new section
    capacity: 100  # set the capacity to 100
  metadata:
    labels:
      mode: deathmatch
    annotations:
      map:  garden22   

Describe alternatives you've considered

We could not do this, and people could pass in a label/annotation to the GameServer, and have it be set by the game server process - but that can take a while, and could introduce more race conditions.

Additional context

• https://agones.dev/site/docs/reference/gameserverallocation/
• https://agones.dev/site/docs/integration-patterns/player-capacity/