feat(act_runner): allow to mount volumes (#756)

### Description of the change

In the act_runner StatefulSet, this allows to mount volumes.

### Benefits

It allows to mount some volumes in any of the two containers, e.g. certificates for a private registry.

### Possible drawbacks

I can't think of any.

### Applicable issues

- Fixes #744

### Checklist

- [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)
- [X] Helm templating unittests are added (required when changing anything in `templates` folder)

Co-authored-by: Xav <grandmou@protonmail.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/756
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>
Co-authored-by: grandmou <grandmou@noreply.gitea.com>
Co-committed-by: grandmou <grandmou@noreply.gitea.com>

templates/gitea/act_runner/statefulset.yaml

@@ -70,6 +70,9 @@ spec:
               name: docker-certs
             - mountPath: /data
               name: data-act-runner
+            {{- with .Values.actions.statefulset.actRunner.extraVolumeMounts }}
+            {{- toYaml . | nindent 12 }}
+            {{- end }}
         - name: dind
           image: "{{ .Values.actions.statefulset.dind.repository }}:{{ .Values.actions.statefulset.dind.tag }}"
           imagePullPolicy: {{ .Values.actions.statefulset.dind.pullPolicy }}
@@ -90,6 +93,9 @@ spec:
           volumeMounts:
             - mountPath: /certs/server
               name: docker-certs
+            {{- with .Values.actions.statefulset.dind.extraVolumeMounts }}
+            {{- toYaml . | nindent 12 }}
+            {{- end }}
       {{- with .Values.actions.statefulset.nodeSelector }}
       nodeSelector:
         {{- toYaml . | nindent 8 }}
@@ -108,6 +114,9 @@ spec:
             name: {{ include "gitea.fullname" . }}-act-runner-config
         - name: docker-certs
           emptyDir: {}
+        {{- with .Values.actions.statefulset.extraVolumes }}
+        {{- toYaml . | nindent 8 }}
+        {{- end }}
   volumeClaimTemplates:
     - metadata:
         name: data-act-runner