Add labels to PVC manifest (#581)

Hi,

 In reference to #580

I noticed that one cannot apply labels to the created PVC with persistance.labels.

The label statement is missing in the template.

best regards,

Oliver.

**helm-chart/templates/gitea/pvc.yaml:**
```
{{- if and .Values.persistence.enabled .Values.persistence.create }}
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: {{ .Values.persistence.claimName }}
  namespace: {{ $.Release.Namespace }}
  annotations:
{{ .Values.persistence.annotations | toYaml | indent 4}}
spec:
...
```
**values.yaml:**

```
persistence:
    ## @param primary.persistence.enabled Enable PostgreSQL Primary data persistence using PVC
    ##
    enabled: true
    ## @param primary.persistence.existingClaim Name of an existing PVC to use
    ##
    existingClaim: ""
    ## @param primary.persistence.mountPath The path the volume will be mounted at
    ## Note: useful when using custom PostgreSQL images
    ##
    mountPath: /bitnami/postgresql
    ## @param primary.persistence.subPath The subdirectory of the volume to mount to
    ## Useful in dev environments and one PV for multiple services
    ##
    subPath: ""
    ## @param primary.persistence.storageClass PVC Storage Class for PostgreSQL Primary data volume
    ## If defined, storageClassName: <storageClass>
    ## If set to "-", storageClassName: "", which disables dynamic provisioning
    ## If undefined (the default) or set to null, no storageClassName spec is
    ##   set, choosing the default provisioner.  (gp2 on AWS, standard on
    ##   GKE, AWS & OpenStack)
    ##
    storageClass: ""
    ## @param primary.persistence.accessModes PVC Access Mode for PostgreSQL volume
    ##
    accessModes:
      - ReadWriteOnce
    ## @param primary.persistence.size PVC Storage Request for PostgreSQL volume
    ##
    size: 8Gi
    ## @param primary.persistence.annotations Annotations for the PVC
    ##
    annotations: {}
    ## @param primary.persistence.labels Labels for the PVC
    ##
    labels: {}
```

### Checklist

<!-- [Place an '[X]' (no spaces) in all applicable fields. Please remove unrelated fields.] -->

- [x] Parameters are documented in the `values.yaml` and added to the `README.md` using [readme-generator-for-helm](https://github.com/bitnami-labs/readme-generator-for-helm)

Co-authored-by: pat-s <pat-s@noreply.gitea.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/581
Reviewed-by: pat-s <pat-s@noreply.gitea.com>
Co-authored-by: Oliver Fueckert <oliver@cubinet.de>
Co-committed-by: Oliver Fueckert <oliver@cubinet.de>

templates/gitea/pvc.yaml

@@ -6,6 +6,8 @@ metadata:
   namespace: {{ $.Release.Namespace }}
   annotations:
 {{ .Values.persistence.annotations | toYaml | indent 4}}
+  labels:
+{{ .Values.persistence.labels | toYaml | indent 4}}
 spec:
   accessModes:
   {{- if gt .Values.replicaCount 1.0 }}