Publish helm charts also as an OCI package (e.g. on GHCR/ECR registry)

[mkilchhofer]

Is your feature request related to a problem?
No

Is your feature request related to a specific Helm chart, if yes mention name of the chart?
All helm charts

Describe the solution you'd like
The helm charts are published using the classic approach with a static webserver and an index.yaml (GitHub pages):

helm repo add eks https://aws.github.io/eks-charts

However in helm 3.8+ the OCI method went GA:

• https://blog.bitnami.com/2023/04/httpsblog.bitnami.com202304bitnami-helm-charts-now-oci.html?m=1
• https://helm.sh/docs/topics/registries/
• https://github.com/helm/helm/releases/tag/v3.8.0

I see two options to use as an OCI mirror:

• GHCR (Github packages)
  You need to think about the Github organizational plan. (Free plan only includes 500MB)
• AWS ECR (where you mostly push your container images)

If you would fully rely on native Github actions to produce these artifacts, the change would be super simple

      - name: Run chart-releaser
        uses: helm/[email protected]
        env:
          CR_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
          CR_GENERATE_RELEASE_NOTES: true

        # ================
        # below this line is relevant for OCI publishing
        # ================

      - name: Login to GitHub Container Registry
        uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Push charts to GHCR
        run: |
          shopt -s nullglob
          for pkg in .cr-release-packages/*; do
            if [ -z "${pkg:-}" ]; then
              break
            fi
            helm push "${pkg}" "oci://ghcr.io/${GITHUB_REPOSITORY_OWNER}/charts"
          done

Source: https://github.com/prometheus-community/helm-charts/blob/4bbd07f308884d44d0edff23ee60da967dc2cd23/.github/workflows/release.yaml#L39C1-L61C15
Also a lot of other CNCF projects are using this approach.

Describe alternatives you've considered
Still using the old approach with the index.yaml and static website.