use min instances 2 everywhere and update reference docs

manifests/configmap.yaml

@@ -18,7 +18,7 @@ data:
   connection_pool_image: "registry.opensource.zalan.do/acid/pgbouncer:master-5"
   # connection_pool_max_db_connections: 60
   # connection_pool_mode: "transaction"
-  # connection_pool_number_of_instances: 1
+  # connection_pool_number_of_instances: 2
   # connection_pool_schema: "pooler"
   # connection_pool_user: "pooler"
   # custom_service_annotations: "keyx:valuez,keya:valuea"

manifests/operatorconfiguration.crd.yaml

@@ -317,7 +317,8 @@ spec:
                   #default: "transaction"
                 connection_pool_number_of_instances:
                   type: integer
-                  #default: 1
+                  minimum: 2,
+                  #default: 2
                 connection_pool_default_cpu_limit:
                   type: string
                   pattern: '^(\d+m|\d+(\.\d{1,3})?)$'

manifests/postgresql.crd.yaml

@@ -84,7 +84,7 @@ spec:
                     - "transaction"
                 numberOfInstances:
                   type: integer
-                  minimum: 1
+                  minimum: 2
                 resources:
                   type: object
                   required: