feat: protect game fleet during voluntary disruption

deploy/k8s/base/game-server-pdb.yaml

@@ -0,0 +1,15 @@
+apiVersion: policy/v1
+kind: PodDisruptionBudget
+metadata:
+  name: cosmic-clash-game
+  namespace: cosmic-clash
+  labels:
+    app.kubernetes.io/name: game-server-pdb
+spec:
+  # Voluntary node drains must preserve the Fleet's two-Ready floor. Agones
+  # remains responsible for replacing an evicted process before more capacity
+  # is voluntarily removed.
+  minAvailable: 2
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: game-server

deploy/k8s/base/kustomization.yaml

@@ -8,3 +8,4 @@ resources:
   - control-plane-deployment.yaml
   - fleet.yaml
   - fleet-autoscaler.yaml
+  - game-server-pdb.yaml