Prevent gitea pods from being co-scheduled

For scale out purposes, we only want one gitea pod per underlying
kubernetes node. Use podAntiAffinity to accomplish this.

Change-Id: Icd8f70cf7e1640e58133f67e8a519267ac3b36d3

kubernetes/gitea/k8s/deployment.yaml

@@ -71,3 +71,13 @@ spec:
         - name: secrets
           secret:
             secretName: gitea-app
+      affinity:
+        podAntiAffinity:
+          requiredDuringSchedulingIgnoredDuringExecution:
+            - labelSelector:
+                matchExpressions:
+                  - key: app
+                    operator: In
+                    values:
+                      - gitea
+              topologyKey: "kubernetes.io/hostname"