Implement remote chart

[ranjith-ka]

Fixes: #nnn
Related: N/A
Merge before/after: N/A

Description

This PR adds support for using values files that are co-located inside remote Helm charts (such as those from OCI registries or remote repositories) in Skaffold.

• Users can now specify a values file from a remote chart using the special :chart: prefix in the valuesFiles list.
• Skaffold will pull the remote chart, extract the specified file, and use it as a values file override during deployment.
• Documentation has been updated to describe the new feature, usage, and limitations.

User facing changes

Before:

• Users could only use local values files with remote Helm charts.
• It was not possible to reference additional values files (e.g., values-prod.yaml) that exist only inside the remote chart.

After:

• Users can specify :chart:values-prod.yaml in valuesFiles to use a values file from inside the remote chart.
• Example:

  deploy:
    helm:
      releases:
        - name: my-remote-release
          remoteChart: oci://harbor.example.com/myrepo/mychart
          version: 1.2.3
          valuesFiles:
            - ":chart:values-prod.yaml"

• Skaffold will automatically pull the chart, extract the file, and use it for deployment.

Documentation

• The Helm deployer documentation (docs-v2/content/en/docs/deployers/helm.md) has been updated with usage instructions, an example, and limitations for the new feature.

Follow-up Work

• Add integration tests for this feature (if not already present).
• Consider supporting subdirectories or more advanced file selection in the future.

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[gemini-code-assist]

Summary of Changes

Hello @ranjith-ka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances Skaffold's Helm deployer capabilities by introducing support for using values files that are bundled directly within remote Helm charts. This allows users to more seamlessly manage and deploy applications where specific configurations are co-located with the chart itself, streamlining the deployment process for remote chart users.

Highlights

• New Feature: Remote Chart Values Files: Skaffold now supports referencing valuesFiles directly from within remote Helm charts (e.g., OCI registries or remote repositories), allowing users to use configurations co-located with their charts.
• :chart: Prefix Support: Users can specify ":chart:filename.yaml" in their valuesFiles list within skaffold.yaml to instruct Skaffold to extract a specific values file from the remote chart.
• Automated Chart Pull and Extraction: Skaffold will automatically pull the specified remote chart, extract the designated values file to a temporary location, and use it as an override during deployment, with proper cleanup.
• Documentation Update: The Helm deployer documentation (docs-v2/content/en/docs/deployers/helm.md) has been updated to clearly describe the new feature's usage, provide examples, and outline its current limitations.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable feature for Skaffold users by allowing the use of values files directly from remote Helm charts. The implementation is well-contained within a new utility function and integrated cleanly into the existing deployment logic. The accompanying documentation is clear and provides good examples. My review focuses on correctness, maintainability, and code hygiene. Overall, this is a great contribution. Addressing the feedback below will make the new feature more robust and easier to maintain.

[gemini-code-assist]

The current logic using filepath.Base(hdr.Name) is too broad. It will match any file with the given name, regardless of its location within the chart archive. This can lead to unexpected behavior, as the documentation states that "The file must exist in the root of the chart archive". The logic should be more strict to only match files in the top-level directory of the chart (e.g., mychart/values.yaml).

Suggested change

	if filepath.Base(hdr.Name) == fileInChart {
	pathParts := strings.Split(filepath.ToSlash(hdr.Name), "/")
	if hdr.Typeflag == tar.TypeReg && len(pathParts) == 2 && pathParts[1] == fileInChart {