[Feature]: Publish the gpu-operator Helm chart as an OCI artifact

[Tanguille]

Feature description

The gpu-operator Helm chart is currently distributed only via the classic Helm repository at https://helm.ngc.nvidia.com/nvidia. This is a request to additionally publish it as an OCI artifact (e.g. to nvcr.io or ghcr.io).

Motivation

OCI is the recommended distribution mechanism for Helm charts and is increasingly expected by GitOps tooling:

• Flux's OCIRepository supports digest pinning and cosign/notation signature verification at the source level — not possible with a classic HelmRepository.
• OCI charts can be mirrored, proxied, and air-gapped with standard registry tooling, and verified with standard supply-chain tools (relevant to Publish keyless cosign signatures, SLSA provenance, and SBOM attestations for releases #2432).
• Environments that consume all charts via OCI currently have to special-case gpu-operator.

Prior discussion

This was previously requested in #521, which was closed as completed with a link to the NGC catalog page. That page still serves the classic https:// Helm repo rather than an OCI artifact, and nvcr.io/nvidia/gpu-operator currently contains only container images, no chart — a point also raised by commenters on #521 after it was closed.

In the meantime, the chart is being mirrored to OCI at home-operations/charts-mirror as a stop-gap until an official OCI artifact is available.