Rename bind DNS namespaces to ns-*

Renames the three BIND DNS app namespaces from binddns-* to ns-* (the
ApplicationSet derives each app's namespace from its overlay directory
name, so the registration and destinations move with the rename). The
matching overlay dirs are renamed in the per-tier PRs.

- applicationset: apps/overlays/*/binddns-{auth,resolver,externaldns}
  -> ns-{auth,resolver,externaldns}
- project: binddns-* destinations -> ns-*

argocd/projects/platform.yaml

@@ -21,11 +21,11 @@ spec:
       server: https://kubernetes.default.svc
     - namespace: 'authentik'
       server: https://kubernetes.default.svc
-    - namespace: 'binddns-auth'
+    - namespace: 'ns-auth'
       server: https://kubernetes.default.svc
-    - namespace: 'binddns-resolver'
+    - namespace: 'ns-resolver'
       server: https://kubernetes.default.svc
-    - namespace: 'binddns-externaldns'
+    - namespace: 'ns-externaldns'
       server: https://kubernetes.default.svc
     - namespace: 'cert-manager'
       server: https://kubernetes.default.svc