allow templating of volumes (#12734)

Rendering the volumes using the tpl function allows templating within values.yaml

If one for example renders a secret or config-map within a chart which has this chart
declared as dependency in its `requirements.yaml` then one could inject the rendered
secret like this:

```
Persistence:
  volumes:
  - name: jenkins-secrets
    secret:
      secretName: '{{ template "jenkins.fullname" . }}-casc-secrets'
  mounts:
  - mountPath: /run/secrets/casc
    name: jenkins-secrets
    readOnly: true
```

Signed-off-by: Torsten Walter <mail@torstenwalter.de>

stable/jenkins/Chart.yaml

@@ -1,6 +1,6 @@
 name: jenkins
 home: https://jenkins.io/
-version: 0.36.2
+version: 0.36.3
 appVersion: lts
 description: Open source continuous integration server. It supports multiple SCM tools
   including CVS, Subversion and Git. It can execute Apache Ant and Apache Maven-based

stable/jenkins/templates/jenkins-master-deployment.yaml

@@ -316,7 +316,7 @@ spec:
 
       volumes:
 {{- if .Values.Persistence.volumes }}
-{{ toYaml .Values.Persistence.volumes | indent 6 }}
+{{ tpl (toYaml .Values.Persistence.volumes | indent 6) . }}
 {{- end }}
       - name: plugins
         emptyDir: {}