feat(whiteboard): Add optional whiteboard backend Deployment

[Shevonar]

Description of the change

This PR adds an option to deploy the backend server for the Nextcloud Whiteboard app. It also includes another ingress to expose the backend server to the user. A startup hook automatically configures the required URL and JWT_SECRET_KEY for the Nextcloud Whiteboard app to connect to the backend server.

Benefits

This change provides an easy way to deploy the Whiteboard backend.

Possible drawbacks

Unless whiteboard.enabled is set to true nothing will change.

Applicable issues

• closes #701

Additional information

I tested this change on my personal Nextcloud instance where I run with Ingresses and TLS enabled. I'm not sure if there need to be additional adjustments for other setups.

Checklist

• [x] I have read the CONTRIBUTING.md doc.
• [x] DCO has been signed off on the commit.
• [x] Chart version bumped in Chart.yaml according to semver.
• [x] (optional) Parameters are documented in the README.md