Feature Request: Add persistent cache support using actions/cache

[mridang]

Feature request

The setup-helm action currently only uses the runner's local tool cache (/opt/hostedtoolcache/) which does not persist across different GitHub Actions runners. This means Helm is re-downloaded on every workflow run, even when using the same version.

Unlike other setup actions (e.g., actions/setup-go, actions/setup-node), the Helm installation is not visible in GitHub's cache dashboard and cannot be shared across workflow runs. This results in:

• Slower workflow runs due to repeated downloads
• Increased bandwidth usage
• Inconsistent behavior compared to other GitHub setup actions

Users can currently work around this by manually adding an actions/cache step before setup-helm, but this requires understanding the internal cache directory structure and adds boilerplate to every workflow.

Solution

Integrate @actions/cache directly into the action to enable persistent caching across workflow runs. This would:

• Add @actions/cache as a dependency
• Restore the cache from GitHub's cache storage before checking the local tool cache
• Save the cache after successful Helm installation
• Make cached Helm installations visible in the repository's cache dashboard

This could be implemented as an opt-in or opt-out feature via a new input parameter:

- uses: azure/setup-helm@v4
  with:
    version: 'v3.18.4'
    cache: true  # Enable persistent caching (could default to true)

The cache key should include the OS, architecture, and Helm version to ensure correct cache invalidation when any of these change.

[chadxz]

I came here to post this. Especially relevant when stuff like this happens: #226