fix(argocd): deploying cert-manager webhooks requires kube-system

To deploy a cert-manager webhook we need to be able to create a
rolebinding in kube-system so access must be granted here.

Author: cardoe

apps/appsets/understack.yaml

@@ -92,6 +92,8 @@ spec:
     server: '*'
   - namespace: 'global-secrets-sync'
     server: '*'
+  - namespace: 'kube-system'
+    server: '*'
   clusterResourceWhitelist:
   - group: '*'
     kind: '*'