chore(thin,cloudpg): scale down to 1 replica, disable PDB

kubernetes/thin/apps/database/postgresql/cluster/cluster16.yaml

@@ -6,7 +6,8 @@ metadata:
   name: postgres16
   namespace: database
 spec:
-  instances: 3
+  instances: 1
+  enablePDB: false # NOTE: enable when instances > 1
   imageName: ghcr.io/tensorchord/cloudnative-pgvecto.rs:16.4 #ghcr.io/cloudnative-pg/postgresql:16.4-28
   primaryUpdateStrategy: unsupervised
   storage:
@@ -22,7 +23,6 @@ spec:
       max_connections: "400"
       shared_buffers: 256MB
     enableAlterSystem: true # must be set to true to enable pgvecto.rs
-  enablePDB: true
   resources:
     requests:
       cpu: 20m