Add `RpcAgentOptions` struct type, which bundles different required arguments for different `RpcAgent`s (#29972)
Summary:
https://github.com/pytorch/pytorch/pull/28226 introduced `worker_to_id` arg to the `def init_rpc` function for other `RpcAgent`. While it's not really used by `ProcessGroupAgent`. Cleanup is wanted for this, as described in https://github.com/pytorch/pytorch/issues/29031.
To adapt to the difference of different `RpcAgent`, adding a `RpcAgentOptions` base classes, which allow leveraging inheritance to add extra fields.
closes https://github.com/pytorch/pytorch/issues/29031
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29972
Differential Revision: D18549919
Pulled By: xush6528
fbshipit-source-id: b9f3f1a41d1ff18498734081870820b055d56f5b
