Creates a singleton class for GitClient rather than relying on creating an instance to
require being passed around throughout its usages.
PR Close#41515
Instead of repeating the logic for adding the github token to
a repository git url, we add a shared function for automatically
computing the URls with token.
Additionally, URLs for updating/generating tokens have been moved
to a dedicated file in the `utils` folder. Also while being at it,
the yargs github token helper is also moved into the dedicated
Git/Github related util folder.
PR Close#38656
