Add OCI publishing for Helm charts to GHCR

[willianpaixao]

Pull Request Description

What type of PR is this?

/kind feature
/area helm-charts
/area cluster-autoscaler

What this PR does / why we need it:

This PR adds OCI (Open Container Initiative) publishing for Helm charts to GitHub Container Registry (GHCR).

Helm 3.8+ supports OCI-based chart distribution as a GA feature, and many CNCF projects have adopted this approach (e.g., prometheus-community/helm-charts). This provides users with an alternative installation method that doesn't require adding a Helm repository first.

Changes:

• Updated .github/workflows/chart-release.yaml to push charts to GHCR after release
• Upgraded Helm from v3.4.0 to v3.19.2 (OCI support requires 3.8+)
• Added packages: write permission for GHCR access
• Updated chart READMEs with OCI installation instructions

After this change, users can install charts via:

helm install my-release oci://ghcr.io/kubernetes/charts/cluster-autoscaler
helm install my-release oci://ghcr.io/kubernetes/charts/vertical-pod-autoscaler

The classic Helm repository continues to work alongside OCI.

Which issue(s) this PR fixes:

Fixes #7086

Special notes for your reviewer:

• The implementation follows the pattern used by prometheus-community/helm-charts
• No changes to chart structure or content are required
• Uses the existing GITHUB_TOKEN secret already available in the workflow

Does this PR introduce a user-facing change?

Helm charts are now published as OCI artifacts to ghcr.io/kubernetes/charts. Users with Helm can install charts directly via `helm install my-release oci://ghcr.io/kubernetes/charts/cluster-autoscaler` without adding a Helm repository first.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

• Helm OCI Support
• Chart Releaser Action

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[k8s-ci-robot]

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[Copilot]

Pull request overview

This PR adds OCI (Open Container Initiative) publishing support for Helm charts to GitHub Container Registry (GHCR), enabling users to install charts directly without adding a Helm repository first. The implementation upgrades the Helm version to support OCI features and adds new workflow steps to push released charts to GHCR.

Key changes:

• Added OCI publishing workflow steps with GHCR authentication and chart push logic
• Upgraded Helm from v3.4.0 to v3.19.2 and updated GitHub Actions dependencies
• Updated chart READMEs with OCI installation instructions alongside existing Helm repository method

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
.github/workflows/chart-release.yaml	Added GHCR login and chart push steps for both CA and VPA jobs; upgraded action versions and Helm version; added packages: write permission
cluster-autoscaler/charts/cluster-autoscaler/README.md	Added "Using OCI Registry" section with helm install examples for both autodiscovery and manual configuration methods
vertical-pod-autoscaler/charts/vertical-pod-autoscaler/README.md	Added "Installation" section with both Helm repository and OCI registry installation methods

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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[willianpaixao]

/assign gjtempleton

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: willianpaixao
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