Self-serve device pool configuration

[huydhn]

Some of the common activities from ExecuTorch are to:

1. Add/remove devices from existing pools
2. Create new device pool

I have written a wiki on how to do this via AWS console UI https://github.com/pytorch/executorch/wiki/How-to-create-a-custom-device-pool-on-AWS-Device-Farm. However, this method generally depends on Dev Infra team to pick up the request, which doesn't scale well. We need to figure out a way to give ExecuTorch the the configure their device pools themselves.

Some potential solutions:

• To use JSON or YAML configuration to manage device pools
• Build an UI on HUD to mirror https://github.com/pytorch/executorch/wiki/How-to-create-a-custom-device-pool-on-AWS-Device-Farm without the need to explicitly grant people access to AWS