[stable/postgresql] Fix NetworkPolicy in replicated mode (helm#13863)

* stable/postgresql: Fix NetworkPolicy in replicated mode

With replication enabled and a network policy that prevents external
communication, i.e.

```yaml
replication:
  enabled: true
networkPolicy:
  enabled: true
  allowExternal: false
```

the slave pods are not allowed to connect to the master, which causes
them to enter into a crash loop.

This commit expands the ingress policy to allow communication from the
slaves to the master on port 5432.

Signed-off-by: Benoît Knecht <benoit.knecht@fsfe.org>

* stable/postgresql: Bump chart version number to 4.2.2

Signed-off-by: Benoît Knecht <benoit.knecht@fsfe.org>

stable/postgresql/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: postgresql
-version: 4.2.1
+version: 4.2.2
 appVersion: 10.8.0
 description: Chart for PostgreSQL, an object-relational database management system (ORDBMS) with an emphasis on extensibility and on standards-compliance.
 keywords:

stable/postgresql/templates/networkpolicy.yaml

@@ -22,6 +22,11 @@ spec:
       - podSelector:
           matchLabels:
             {{ template "postgresql.fullname" . }}-client: "true"
+      - podSelector:
+          matchLabels:
+            app: {{ template "postgresql.name" . }}
+            release: {{ .Release.Name | quote }}
+            role: slave
     {{- end }}
     # Allow prometheus scrapes
     - ports: