:new 🔧 git: Improve git sync-fork aliases for default git branch

This commit reworks my git alias to sync up a local repository as a "middleware" of sorts between two remote git repositories. One alias worked fine, but was hard-coded to use master and most of my git projects seem to use main these days.

That said, there are always exceptions to the norm. So I added a new function-driven alias that will sync a fork with a custom remote and custom branch name, if I ever get into an unwieldy situation. 😉