REFACTOR(postgresql): change pg anti-affinity

- from hard to soft
- Use podAntiAffinityType: preferred instead of required
- Allows pods to be scheduled on same node if necessary

postgresql/manifests/cluster.yaml

@@ -65,9 +65,9 @@ spec:
 
   # Backup disabled - using Velero for backups instead
 
-  # Affinity to spread replicas across nodes
+  # Affinity to spread replicas across nodes (soft - prefer different nodes)
   affinity:
-    podAntiAffinityType: required
+    podAntiAffinityType: preferred
     tolerations:
       - key: "node-role.kubernetes.io/master"
         operator: "Exists"