Ability to inflate helm chart to a git path during promotion

[jessesuen]

Proposed Feature

Today, when using a helm chart subscription, kargo has the following two ways to promote a new chart that is pushed to a helm chart repository:

1. Non-gitops: update a live argocd app spec with the new semvers
2. GitOps: update a subchart in an umbrella chart at a git path

These have the following drawbacks:

• Option 1 is not really gitops, and specific to Argo CD
• While Option 2 is gitops, it forces the use of an umbrella chart, which has the drawback of dependent values being nested under a field in the top values.yaml.

Kargo should provide a third option, which would download and untar the full helm chart to a chosen location in git.

Motivation

One use case is to avoid the use of the umbrella chart, which seems unnecessary when there is a single chart needs to be promoted.

Users of Kustomize's chart inflator would benefit from fully inflated charts in git.

Suggested Implementation

As an alternative to updating the semvers of a file in git, extract the helm tarball to a specified location.

[krancour]

This would be something we can tackle more easily after #2219. i.e. It will just be another built-in step. Tentatively putting this in v0.10.0.