Upload Helm chart to OCI registry

[onedr0p]

With Helm v3.8.0, the OCI support became GA, which is an excellent chance to start publishing Helm charts to OCI-compliant registries. Quay / Dockerhub / GHCR supports OCI artifacts and a lot of projects have been using them to publish their helm charts as OCI artifacts.

It brings an opportunity to sign Helm charts stored as OCI Artifacts with cosign to provide their integrity and use GitOps tooling such as Flux to reconcile them as they were stored as OCI artifacts. Flux can reconcile OCI Artifacts and verify their integrity before reconciling them.