Add support for Git Credential Manager on Windows

In order to make Git experience better for GitLab and GitLab self-hosted users, it would be great if support for Git Credential Manager could be added. I created an issue on GitHub's repo - https://github.com/Microsoft/Git-Credential-Manager-for-Windows/issues/480. Would anyone from GitLab be interested in contributing the code there?

It would generally make the Git flow for 2FA / social login users much more easier and secure - they don't have to deal with tokens or passwords and instead, they just sign in through their familiar prompt.