Deploy cephrgw-operator to cephrgw-system

The cephrgw-operator provisions Ceph RGW (S3) buckets and access keys from
CRDs via the Ceph manager dashboard API. Deploy it as a platform app.

- Add apps/base/cephrgw-system: namespace, ServiceAccount + ClusterRole/
  Binding (manage ceph.unkin.net CRDs, Secrets, leases), and the operator
  Deployment. CRDs are pulled from the operator repo at tag v0.1.0; the
  Deployment sources dashboard credentials from the cephrgw-credentials
  Secret via envFrom and carries the reloader annotation.
- Add apps/overlays/au-syd1/cephrgw-system referencing the base.
- Register apps/overlays/*/cephrgw-system in the platform ApplicationSet.

The platform AppProject already permits *-system namespaces and the
Namespace/ClusterRole/CRD cluster resources, so no project change is needed.
Requires the cephrgw-credentials Secret to be created out-of-band (see the
operator's docs/ceph-setup.md); it is intentionally not managed in GitOps.

argocd/applicationsets/platform.yaml

@@ -18,6 +18,7 @@ spec:
       - path: apps/overlays/*/cattle-system
       - path: apps/overlays/*/cert-manager
       - path: apps/overlays/*/certificates
+      - path: apps/overlays/*/cephrgw-system
       - path: apps/overlays/*/cnpg-system
       - path: apps/overlays/*/consul
       - path: apps/overlays/*/elastic-system