Setup Automatic Rebase given a /rebase comment (#34369)

Summary:
This is a nit, but at least will help us reduce requests to rebase for PRs which maybe have a broken CI due to a stale base commit.

I've limited the scope to members and owners. A `/rebase` will trigger a rebase authored by Github Action bot.

We can play a bit around with it, and remove it if it doesn't really work well for us.

## Changelog

[Internal] - Setup Automatic Rebase given a /rebase comment

Pull Request resolved: https://github.com/facebook/react-native/pull/34369

Test Plan: Nothing to test here.

Reviewed By: cipolleschi

Differential Revision: D38509480

Pulled By: cortinico

fbshipit-source-id: 1df3927638b162d4a787c81372a835d583159498