Update helm-release.yml workflow to also push as OCI

[petewall]

Here's a change to the grafana/helm-charts repo that involves pushing charts as OCI to ghcr.io: https://github.com/grafana/helm-charts/pull/2998/files.

We could do the same in our helm-release.yml. This would give users the option to install with:

• helm repo add ...
• helm repo update
• helm install grafana/k8s-monitoring
  OR
• helm install oci://...

[danielbraun89]

Please implement this!
linking grafana/helm-charts#2395