cephrgw-system: source cephrgw-credentials from Vault via VSO

Replace the out-of-band cephrgw-credentials Secret with a VSO-managed one so
the operator's Ceph dashboard credentials come from Vault.

- Add apps/base/cephrgw-system/vaultauth.yaml: VaultAuth (k8s/au/syd1 mount,
  role cephrgw-operator, SA cephrgw-operator, connection vso-system/default).
- Add apps/base/cephrgw-system/vaultstaticsecret.yaml: renders the KV path
  service/cephrgw/dashboard-credentials into the cephrgw-credentials Secret
  (keys copied verbatim, consumed by the Deployment via envFrom).
- Reference both from the base kustomization.

Requires the Vault role/policy from terraform-vault #95 and the KV values to
be seeded (see the operator's docs/ceph-setup.md).

apps/base/cephrgw-system/vaultstaticsecret.yaml

@@ -0,0 +1,21 @@
+---
+# Renders the Ceph dashboard credentials from Vault into the cephrgw-credentials
+# Secret the operator Deployment consumes via envFrom. The KV secret's keys
+# (CEPH_DASHBOARD_URL/USERNAME/PASSWORD, optional CEPH_RGW_ENDPOINT/CA) are
+# copied verbatim, so they land as the matching env vars.
+apiVersion: secrets.hashicorp.com/v1beta1
+kind: VaultStaticSecret
+metadata:
+  name: cephrgw-credentials
+  namespace: cephrgw-system
+spec:
+  vaultAuthRef: default
+  mount: kv
+  type: kv-v2
+  path: service/cephrgw/dashboard-credentials
+  refreshAfter: 5m
+  hmacSecretData: true
+  destination:
+    name: cephrgw-credentials
+    create: true
+    overwrite: true