mailmap: Move feature into a dedicated django application
Move all templates, views, urls and commands related to the mailmap feature into its dedicated django application.
Please note that the initial migration will not perform any database operations as the tables have already been created by the swh.web.auth django application the mailmap feature was previously located at.
Related to #4398 (closed)
Depends on !869 (closed)
Migrated from D8266 (view on Phabricator)