feat(ci): add release workflow for Helm charts

[luizfelmach]

What kind of change does this PR introduce?

This PR introduces the initial setup for publishing Supabase Helm charts via a Helm repository, enabling simple installation and automated releases.

What is the current behavior?

Currently, there is no official Helm repository configured for this project, which means:

• Helm charts cannot be installed via helm repo add
• There is no automated versioning or release process
• Charts must be built and distributed manually

This work builds on previous discussions and attempts, but no solution was merged at the time.

What is the new behavior?

With this change:

• A Helm repository is published and can be consumed directly via Helm:

helm repo add supabase https://supabase-community.github.io/supabase-kubernetes
helm install supabase supabase/supabase

• Releases are automatically versioned using Git tags
• Charts are built by CI and published to GitHub Artifacts
• The Helm repository index (index.yaml) is tracked via the gh-pages branch
• This enables a simple, repeatable, and reliable deployment workflow for users

Additional context

• This PR was inspired by the discussion in:

  • Issue: helm chart easier to install and works with terraform #76

• Special thanks to the contributors of the previous proposal:

  • PR: Publish helm chart using github pages #97
    Although it was closed without being merged, it provided valuable context and helped shape this implementation.
  • PR: Add GitHub Action for chart release #55

• The CI pipeline is responsible for:

  • Building the Helm chart
  • Tagging releases automatically
  • Publishing chart artifacts to GitHub Artifacts
  • Updating the Helm repository index

• Important:
  Before merging this PR, a gh-pages branch must be created to track the index.yaml file used by the Helm repository.

Steps:

git checkout main
git checkout -b --orphan gh-pages
git rm -rf .
git checkout main -- LICENSE
git add LICENSE
git commit -m "Initial setup"
git push origin gh-pages

• This setup significantly simplifies:
  • Deployments
  • Upgrades
  • Release management
  • Consumption by external users and automation tools