Add Git `.mailmap` file (#4138)

This PR adds a Git [`.mailmap`](https://git-scm.com/docs/gitmailmap)
file to canonicalize committer names/emails.

Release Notes:

- N/A

Marshall Bowers committed 2y ago

93a567adfbdf552316f5715649732f2e45db5c9c

Parent: b0db384

Committed by GitHub <noreply@github.com> on 1/18/2024, 10:38:28 PM