Add git mailmap (#15396)

Canonicalize author and commiter names and addresses via git mailmap.

https://git-scm.com/docs/gitmailmap

.mailmap

@@ -0,0 +1,17 @@
+Ary Borenszweig <[email protected]> <[email protected]>
+Ary Borenszweig <[email protected]> <[email protected]>
+Ary Borenszweig <[email protected]> <[email protected]>
+Brian J. Cardiff <[email protected]> <[email protected]>
+Brian J. Cardiff <[email protected]> <[email protected]>
+George Dietrich <[email protected]> <[email protected]>
+George Dietrich <[email protected]> <[email protected]>
+Gustavo Giráldez <[email protected]> <[email protected]>
+Johannes Müller <[email protected]> <[email protected]>
+Juan Wajnerman <[email protected]> <[email protected]>
+Juan Wajnerman <[email protected]> <[email protected]>
+Juan Wajnerman <[email protected]> <[email protected]>
+Julien Reichardt <[email protected]> <[email protected]>
+Martin Verzilli <[email protected]> <[email protected]>
+Matías García Isaía <[email protected]> <[email protected]>
+Matías García Isaía <[email protected]> <[email protected]>
+Stephanie Hobbs <[email protected]> <[email protected]>