[FEAT]: Support merge-upstream / sync fork endpoint

[mdanish-kh]

Describe the need

Support sync fork endpoint from GitHub API: https://docs.github.com/en/rest/branches/branches?apiVersion=2022-11-28#sync-a-fork-branch-with-the-upstream-repository

Issue #1833 described a way to do that without the GitHub API, but as this comment may explain, the API maybe really wasn't meant for that usage - and we've seen issues with the usage of that API

Refs:

• Bug - Fork Sync Issue microsoft/winget-create#502
• BREAKING BEHAVIOR: WingetCreate fails to create a pull request microsoft/winget-create#580

As such - I would like to see the /merge-upstream GitHub endpoint supported in the Client SDK

SDK Version

No response

API Version

2022-11-28

Relevant log output

No response

Code of Conduct

• I agree to follow this project's Code of Conduct