Support git/tarball based helm chart repos

[nesl247]

Problem description

HashiCorp's official helm chart at https://github.com/hashicorp/vault-helm does not actually have an index.yaml because they do not have a proper setup. With this in mind, we cannot specify a helm chart without having previously downloaded the chart ourselves.

Suggestions for a fix

Add the ability to clone repositories and specify tarball URLs that will not execute helm repo add. Essentially, add a way to automatically download/clone an endpoint without having to setup a proper helm chart.

[marcus-sa]

Is this on the roadmap..?

[EronWright]

The provider has some functionality along these lines:

1. It supports the use of a tarball file or URL in the chart property, avoiding the need to add a repository.
2. It supports proper Helm repositories that are either pre-added or used directly.

This issue is about supporting source-based chart repositories, e.g. cloning a git repository. Helm has plugins for this, e.g. aslafy-z/helm-git.