chore(argocd): allow external-dns namespace

Author: skrobul

apps/appsets/project-understack-operators.yaml

@@ -16,6 +16,8 @@ spec:
     server: '*'
   - namespace: 'cnpg-system'
     server: '*'
+  - namespace: 'external-dns'
+    server: '*'
   - namespace: 'external-secrets'
     server: '*'
   - namespace: 'rook-ceph'