Add OCI repository publish to ghcr.io for helm charts released from other repositories

[krajorama]

Followup to #2998 #2395

Implement releasing LGTM databases and other helm charts to github packages.
Update
https://github.com/grafana/helm-charts/blob/main/.github/workflows/update-helm-repo.yaml

[benoitschipper]

Hey All, I see there are already some Helm Charts being published as OCI Artifact (packages) here: https://github.com/orgs/grafana/packages?repo_name=helm-charts , or even within their own respective project within the grafana/*** github page.

I'd love to be able to also collect the following Helm Charts through GHCR as OCI Artifact:

• Loki - Helm Chart: https://github.com/grafana/loki/tree/main/production/helm/loki
• Mimir Distributed - Helm Chart: https://github.com/grafana/mimir
• Pyroscope - Helm Chart: https://github.com/grafana/pyroscope/tree/main/operations/pyroscope/helm/pyroscope
• Alloy - Helm Chart: https://github.com/grafana/alloy/tree/29baf3fd21a26e6004d9fef8221035db155b63db/operations/helm/charts/alloy
• Beyla - Helm Chart: https://github.com/grafana/beyla/tree/main/charts/beyla

The reason I like the OCI artifact has to do with the fact that I often require to work within airgapped environments. If the helm charts are available as OCI artifacts it allows me to gather and airgap these helm charts as OCI artifacts, the same way as I do with Images from multiple artifact repo's such as Docker/GHCR and more. Using tooling such as Skopeo Sync and Renovate to automatically alert me of a new version and decrease the amount of LCM.

Hope this makes sense! <3