[torchx.pipelines] Add Argo Workflows pipeline adapter

[kiukchung]

Description

Add support for adapting torchx.AppDefs to Argo's "Template" (https://argoproj.github.io/argo-workflows/workflow-concepts/)

Motivation/Background

torchx-0.1.0dev only support Kubeflow pipelines.

Detailed Proposal

Add https://github.com/pytorch/torchx/tree/master/torchx/pipelines/kfp for Argo Workflows

Alternatives

N/A

Additional context/links

N/A

[d4l3k]

KFP pipeline specs are built on Argo so should be fairly straightforward to add support.

Argo also can plug launch Volcano jobs so we can get distributed for free existing kubernetes scheduler support https://github.com/volcano-sh/volcano/blob/master/example/integrations/argo/README.md