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/06-zones.yaml

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: fancy-dns-zones
+  namespace: dns
+  labels:
+    app.kubernetes.io/name: fancy-dns
+    app.kubernetes.io/component: local-zones
+# Leave data unmanaged by GitOps. The Local zones page writes one
+# zone--<apex>.zone
+# key per zone through the API; server-side apply preserves those user fields.