rework postgres storage to single-replica best-effort

manifests/postgres/statefulset.yaml

@@ -50,7 +50,7 @@ spec:
         - name: PGDATA
           value: /var/lib/postgresql/data/pgdata
         volumeMounts:
-        - name: postgres-storage
+        - name: postgres-local
           mountPath: /var/lib/postgresql/data
           subPath: pgdata # Using subPath to avoid permission issues
         - name: dshm
@@ -60,6 +60,8 @@ spec:
         - name: postgres-config-volume
           mountPath: /etc/postgresql/postgresql.conf
           subPath: postgresql.conf
+        - name: postgres-local
+          mountPath: /mnt
         command:
         - docker-entrypoint.sh
         - -c
@@ -114,4 +116,7 @@ spec:
           name: postgres-config
       - name: postgres-storage
         persistentVolumeClaim:
-          claimName: postgres-pvc
+          claimName: postgres-pvc
+      - name: postgres-local
+        persistentVolumeClaim:
+          claimName: postgres-local-pvc