[torchx.component] Implement an HPO component + app

[kiukchung]

Description

Support HPO as a builtin component.

Motivation/Background

Detailed Proposal

The HPO app needs to be implemented (TODO -> attach a detailed design doc RFC), and an appropriate AppDef should be authored and placed in torchx.components.hpo so that it is available as a builtin.

The HPO optimizer itself can be one of: botorch (https://botorch.org/) or ax (https://ax.dev/).

Alternatives

N/A

Additional context/links

N/A

[d4l3k]

initial POC code for HPO #159

[kiukchung]

offering HPO as runtime module for now.