Implement gitmailmap

Maintaining clean and consistent set of authors

See:

• https://git-scm.com/docs/gitmailmap
• https://improveandrepeat.com/2019/06/little-git-tricks-use-mailmap-to-merge-different-authors/

This will allow map multiple mails and usernames unto one user, and (hopefully) fix the mess we have here:
https://git.jinr.ru/nica/mpdroot/-/graphs/dev