ci(*): update helm chart releasing

[vdice]

Describe your changes

• Update the helm-chart-release.yml workflow to publish to the ghcr.io registry (e.g. ghcr.io/spinkube/charts/runtime-class-manager)
  • Per description on Helm chart CD #236, this moves from publishing the chart via a chart-releaser GH action (which updates a chart index.yaml via GH pages) and instead publishes it to an OCI registry (ghcr.io)
  • See runs on fork for examples: main and v0.0.1
    • GH Release: https://github.com/vdice/runtime-class-manager/releases/v0.0.1
    • Package listing: https://github.com/vdice/runtime-class-manager/pkgs/container/charts%2Fruntime-class-manager
  • Chart can then be installed via e.g. helm install rcm oci://ghcr.io/vdice/charts/runtime-class-manager
• Add related helm packaging targets to the Makefile
• Add the deploy/update-chart-versions.sh helper script
• Misc. Chart.yaml and README.md updates

Issue ticket number and link

Closes #236

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests.
• I tested the changes with the following distributions:
  • Kind
  • MiniKube
  • MicroK8s
  • Rancher RKE2
  • Azure AKS
  • GCP GKE (Ubuntu nodes)
  • AWS EKS (AmazonLinux2 nodes)
  • AWS EKS (Ubuntu nodes)
  • Digital Ocean Kubernetes

[0xE282B0]

LGTM.