Fix n8n, gitlab, and netbird-operator degraded states

- n8n: Set replicaCount=1 (RWO PVC incompatible with multiple replicas),
  add resource limits to satisfy Kyverno policy
- gitlab: Add ignoreDifferences for redis-gitlab-additional service
  (port names and selectors managed by Redis operator)
- netbird-operator: Add ExternalSecret for netbird-mgmt-api-key in
  netbird namespace and add manifests source to Application

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infrastructure/netbird-operator/manifests/external-secret.yaml

@@ -0,0 +1,18 @@
+apiVersion: external-secrets.io/v1
+kind: ExternalSecret
+metadata:
+  name: netbird-mgmt-api-key
+  namespace: netbird
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    kind: ClusterSecretStore
+    name: vault-backend
+  target:
+    name: netbird-mgmt-api-key
+    creationPolicy: Owner
+  data:
+    - secretKey: NB_API_KEY
+      remoteRef:
+        key: netbird-api-token
+        property: api-token