Add UI editing for local DNS zones

Local zones were only editable as mounted files, so operators could not manage DNS entries from the console. Add a Local zones editor backed by a shared Kubernetes ConfigMap, validate master files before saving, scope the pod service account to that ConfigMap, and reload changed zones on every replica while flushing stale cache entries.

deploy/k8s/kustomization.yaml

@@ -11,6 +11,7 @@ namespace: dns
 resources:
   - 00-config.yaml
   - 05-serviceaccount.yaml
+  - 06-zones.yaml
   - 10-deployment.yaml
   - 20-service.yaml
   - 30-ingress.yaml