[9/n] [torch/elastic] Introduce RendezvousSettings (#56537)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56537
This PR introduces the `RendezvousSettings` type to consolidate the arguments passed to `DynamicRendezvousHandler`.
ghstack-source-id: 127626738
Test Plan: Run the existing unit tests.
Reviewed By: tierex
Differential Revision: D27890155
fbshipit-source-id: 22060c25b6927cc832f18ae6c5f7ba0f7a9ef3cf
