fix minor issues in docs and manifests (#866)

* fix minor issues in docs and manifests
* double retry_timeout_sec

manifests/complete-postgres-manifest.yaml

@@ -24,7 +24,7 @@ spec:
   databases:
     foo: zalando
   postgresql:
-    version: "11"
+    version: "12"
     parameters: # Expert section
       shared_buffers: "32MB"
       max_connections: "10"

manifests/minimal-postgres-manifest.yaml

@@ -16,4 +16,4 @@ spec:
   databases:
     foo: zalando  # dbname: owner
   postgresql:
-    version: "11"
+    version: "12"

manifests/standby-manifest.yaml

@@ -9,7 +9,7 @@ spec:
     size: 1Gi
   numberOfInstances: 1
   postgresql:
-    version: "11"
+    version: "12"
 # Make this a standby cluster and provide the s3 bucket path of source cluster for continuous streaming.
   standby:
     s3_wal_path: "s3://path/to/bucket/containing/wal/of/source/cluster/"