feat: Add release charts workflow

[M0NsTeRRR]

Description

Add a Helm chart release workflow. All charts will be signed using keyless signing (with Cosign) and published to ghcr.io with the image name <chart name>-chart to avoid conflicts with the Jellyseerr Docker image.
The ArtifactHub configuration file will also be signed and pushed to the registry.

You can see an example in my fork :

• Package : https://github.com/M0NsTeRRR?tab=packages&repo_name=jellyseerr
• Workflow : https://github.com/M0NsTeRRR/jellyseerr/actions/runs/12431564343

TO DO

ArtifactHub is a CNCF project—a web-based application for discovering, installing, and publishing packages. Using ArtifactHub will help new users find this Helm chart and provide greater visibility for the project.

1. Create an account at ArtifactHub).
2. Register this repository.
3. Create an artifacthub-repo.yml file in this PR inside the chart folder:

   repositoryID: <REPOSITORY ID>
   owners:
     - name: <Your Name>
       email: <Your Email>

Documentation: ArtifactHub Verified Publisher Guide

Issues Fixed or Closed

• Fixes Official helm chart #1060

[gauthier-th]

@djjudas21 could you please review this too?

[djjudas21]

It's not letting me give an actual review as I don't have write access on the repo, but I've been through the commits and it looks good to me 👌