Add support for Helm charts from OCI registries

[graillus]

Since version 3.8.0 Helm supports OCI registries for chart storage https://helm.sh/docs/topics/registries, but the helm pull command used to fetch a chart from an OCI registry slightly changes, the --repo flag have to be omitted because it only works with http(s) chart repositories. Helm expects the fully-qualified URL to the chart instead as argument.

Proposed Changes

This PR adds support for Helm chart dependencies from OCI registries by removing the --repo flag passed to the helm command when the oci:// prefix is detected in the source property, and pass it as argument instead.

For instance, this configuration:

  kapitan:
    dependencies:
    - type: helm
      output_path: charts/example
      source: oci://europe-west1-docker.pkg.dev/my-project/helm-charts/example
      version: 1.2.3
      chart_name: example

will generate the following Helm command:

helm pull --destination charts/example --untar --version 1.2.3 oci://europe-west1-docker.pkg.dev/my-project/helm-charts/example

[ademariag]

Sweet @graillus ! Thank you, we'll review it!

If you haven't already, join our #kapitan channel on https://kubernetes.slack.com

[ramaro]

Thanks @graillus! LGTM :D