feat: allow inline yaml config instead of string literal (#43)

### Description of the change

Allow to insert the act_runner config as yaml into the chart values.

### Benefits

Yaml editor will report yaml errors, instead of the deployed runner.

### Possible drawbacks

No limitations, string config works like before.

### Applicable issues

N/A

### Additional information

Usage like this, just omit the block scalar token

```yaml
enabled: true
statefulset:
  actRunner:
    # See full example here: https://gitea.com/gitea/act_runner/src/branch/main/internal/pkg/config/config.example.yaml
    config:
      log:
        level: debug
      cache:
        enabled: false
      container:
        valid_volumes:
        - /var/run/docker.sock
        options: -v /var/run/docker.sock:/var/run/docker.sock

## Specify an existing token secret
##
existingSecret: "runner-token2"
existingSecretKey: "token"

## Specify the root URL of the Gitea instance
giteaRootURL: "http://192.168.1.2:3000"
```

I do not like the regex test approach, but I didn't come up with a better one. I wish that I can parse the nested yaml in the helm tests.

### ⚠ BREAKING

N/A

### Checklist

- [x] Helm templating unittests are added (required when changing anything in `templates` folder)
- [x] All added template resources MUST render a namespace in metadata

Reviewed-on: https://gitea.com/gitea/helm-actions/pulls/43
Reviewed-by: DaanSelen <daanselen@noreply.gitea.com>
Co-authored-by: Christopher Homberger <christopher.homberger@web.de>
Co-committed-by: Christopher Homberger <christopher.homberger@web.de>

templates/config-act-runner.yaml

@@ -10,6 +10,10 @@ metadata:
 data:
   config.yaml: |
     {{- with .Values.statefulset.actRunner.config -}}
+    {{- if kindIs "string" . -}}
     {{ . | nindent 4}}
+    {{- else -}}
+    {{ toYaml . | nindent 4}}
+    {{- end -}}
     {{- end -}}
 {{- end }}