feat(hip): OCI Artifact Selection and Referrers Support

[lexfrei]

Summary

This HIP proposes three related enhancements to Helm's OCI support:

1. Artifact Selection from Image Index - Enable helm pull/install/dependency to select chart manifests from OCI Image Index by artifactType (with config.mediaType fallback)

2. Set artifactType on Push - Have helm push set the artifactType field in manifests for efficient selection

3. Referrers API Support - Add --subject flag to helm push for associating charts with container images

Motivation

Current workarounds for publishing charts and images together (tag suffixes like :v1.0.0-helm, separate paths) are unnecessary complexity. OCI 1.1 provides native artifact bundling - Helm should leverage it.

Related

• Issue: helm/helm#31582
• Reference Implementation: helm/helm#31583
• Builds on: HIP-0006 (OCI Support)

Checklist

• [x] HIP follows the template from HIP-0001
• [x] HIP is in draft status
• [x] Reference implementation exists