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.

apps/base/cephrgw-system/deployment.yaml

@@ -0,0 +1,66 @@
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: cephrgw-operator
+  namespace: cephrgw-system
+  labels:
+    app.kubernetes.io/name: cephrgw-operator
+  annotations:
+    # Restart the operator when the credentials Secret rotates.
+    reloader.stakater.com/auto: "true"
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: cephrgw-operator
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: cephrgw-operator
+    spec:
+      serviceAccountName: cephrgw-operator
+      securityContext:
+        runAsNonRoot: true
+      containers:
+        - name: operator
+          image: git.unkin.net/unkin/cephrgw-operator:v0.1.0
+          args:
+            - --metrics-bind-address=:8080
+            - --health-probe-bind-address=:8081
+            - --leader-elect
+          envFrom:
+            # Provides CEPH_DASHBOARD_URL/USERNAME/PASSWORD and, optionally,
+            # CEPH_RGW_ENDPOINT / CEPH_DASHBOARD_CA. Create this Secret per
+            # docs/ceph-setup.md; it is intentionally not managed in GitOps.
+            - secretRef:
+                name: cephrgw-credentials
+          ports:
+            - containerPort: 8080
+              name: metrics
+            - containerPort: 8081
+              name: health
+          readinessProbe:
+            httpGet:
+              path: /readyz
+              port: 8081
+            initialDelaySeconds: 5
+            periodSeconds: 10
+          livenessProbe:
+            httpGet:
+              path: /healthz
+              port: 8081
+            initialDelaySeconds: 15
+            periodSeconds: 20
+          securityContext:
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities:
+              drop: ["ALL"]
+          resources:
+            requests:
+              cpu: 50m
+              memory: 64Mi
+            limits:
+              cpu: 500m
+              memory: 256Mi