Feature Request: Add persistent cache support using actions/cache

### 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:

```yaml
- 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.