Generate the changelog automatically (#50323)

Summary:
This change implements the automatic generation of the Changelog in CI while doing a release.
The output is a PR opened by the react-native-bot that can be manipulated and imported by Meta engineers

## Changelog:
[Internal] - Generate the changelog automatically

Pull Request resolved: https://github.com/facebook/react-native/pull/50323

Test Plan:
Tested as a separated workflow first:
<img width="1624" alt="Screenshot 2025-03-27 at 17 44 47" src="https://github.com/user-attachments/assets/b8877cdb-f63b-4d82-b340-54f612ac0cd4" />
this generated the PR:
https://github.com/facebook/react-native/pull/50328

I also added jest tests:
<img width="516" alt="Screenshot 2025-03-27 at 17 45 39" src="https://github.com/user-attachments/assets/7ebbc310-e41e-48fc-997e-21366c7306cf" />

Reviewed By: cortinico

Differential Revision: D71986909

Pulled By: cipolleschi

fbshipit-source-id: 10ffaf342bb0642a6992a107185b6704815b16e3