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>

values.yaml

@@ -361,13 +361,16 @@ signing:
 ## @param actions.statefulset.nodeSelector NodeSelector for the statefulset
 ## @param actions.statefulset.tolerations Tolerations for the statefulset
 ## @param actions.statefulset.affinity Affinity for the statefulset
+## @param actions.statefulset.extraVolumes Extra volumes for the statefulset
 ## @param actions.statefulset.actRunner.repository The Gitea act runner image
 ## @param actions.statefulset.actRunner.tag The Gitea act runner tag
 ## @param actions.statefulset.actRunner.pullPolicy The Gitea act runner pullPolicy
+## @param actions.statefulset.actRunner.extraVolumeMounts Allows mounting extra volumes in the act runner container
 ## @param actions.statefulset.actRunner.config [default: Too complex. See values.yaml] Act runner custom configuration. See [Act Runner documentation](https://docs.gitea.com/usage/actions/act-runner#configuration) for details.
 ## @param actions.statefulset.dind.repository The Docker-in-Docker image
 ## @param actions.statefulset.dind.tag The Docker-in-Docker image tag
 ## @param actions.statefulset.dind.pullPolicy The Docker-in-Docker pullPolicy
+## @param actions.statefulset.dind.extraVolumeMounts Allows mounting extra volumes in the Docker-in-Docker container
 ## @param actions.statefulset.dind.extraEnvs Allows adding custom environment variables, such as `DOCKER_IPTABLES_LEGACY`
 ## @param actions.provisioning.enabled Create a job that will create and save the token in a Kubernetes Secret
 ## @param actions.provisioning.annotations Job's annotations
@@ -391,11 +394,13 @@ actions:
     nodeSelector: {}
     tolerations: []
     affinity: {}
+    extraVolumes: []
 
     actRunner:
       repository: gitea/act_runner
       tag: 0.2.11
       pullPolicy: IfNotPresent
+      extraVolumeMounts: []
 
       # See full example here: https://gitea.com/gitea/act_runner/src/branch/main/internal/pkg/config/config.example.yaml
       config: |
@@ -408,6 +413,8 @@ actions:
       repository: docker
       tag: 25.0.2-dind
       pullPolicy: IfNotPresent
+      extraVolumeMounts: []
+
       # If the container keeps crashing in your environment, you might have to add the `DOCKER_IPTABLES_LEGACY` environment variable.
       # See https://github.com/docker-library/docker/issues/463#issuecomment-1881909456
       extraEnvs: []