docs(kubernetes): add a more fleshed out example of a Demo Kubernetes cluster

docs/source/distributions/k8s/postgres-k8s.yaml.template

@@ -0,0 +1,67 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: postgres-pvc
+spec:
+  accessModes:
+    - ReadWriteOnce
+  storageClassName: gp2
+  resources:
+    requests:
+      storage: 10Gi
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: postgres
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: postgres
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: postgres
+    spec:
+      containers:
+      - name: postgres
+        image: postgres:15
+        env:
+        - name: POSTGRES_DB
+          value: "${POSTGRES_DB}"
+        - name: POSTGRES_USER
+          value: "${POSTGRES_USER}"
+        - name: POSTGRES_PASSWORD
+          value: "${POSTGRES_PASSWORD}"
+        - name: PGDATA
+          value: "/var/lib/postgresql/data/pgdata"
+        ports:
+        - containerPort: 5432
+        resources:
+          requests:
+            memory: "512Mi"
+            cpu: "250m"
+          limits:
+            memory: "1Gi"
+            cpu: "500m"
+        volumeMounts:
+        - name: postgres-storage
+          mountPath: /var/lib/postgresql/data
+      volumes:
+      - name: postgres-storage
+        persistentVolumeClaim:
+          claimName: postgres-pvc
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: postgres-server
+spec:
+  selector:
+    app.kubernetes.io/name: postgres
+  ports:
+  - protocol: TCP
+    port: 5432
+    targetPort: 5432
+  type: ClusterIP