Generate rich changelog in debugger-frontend sync script, add --no-build flag for testing (#51745)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51745

Changelog: [Internal]

1. Updates debugger-frontend's sync-and-build script to include a simple Markdown changelog inline and -mention authors who are Meta employees.
2. Also adds a `--no-build` flag that is mainly helpful for iterating on changelog generation logic.

Reviewed By: hoxyq

Differential Revision: D75789680

fbshipit-source-id: b30b49a9c50e93e7161a2dad012b92ef124a3a16