Support --post-renderer flag for helm

[musabmasood]

Summary

Helm 3 now supports the --post-renderer flag which is great for last mile modifications of a chart without forking it. It would be great if argocd can support this flag for helm applications.

Motivation

Many a times we want to install a helm chart but its missing some customization e.g. adding a sidecar. Usually we can pass the output of helm template to kustomize and then make these changes.

Since helm now supports the --post-renderer flag, it would be great to use it directly in application.yaml manifests.

Proposal

Since argocd already ships with kustomize, may be the helm specification of the application.yaml can add kustomization support:

    ...
    # helm specific config
    helm:
       kustomizeRenderer: <path/to/kustomization.yaml/in/same/repo>
       valueFiles:
       ...

[crenshaw-dev]

I think this is a duplicate of #3698