mailmap admin interface: only display mailmaps matching a search pattern
Currently, the mailmap admin interface shows a paginated list of all mailmaps.
While this is a very restricted feature that's only available to a small set of users, dumping all the information by default is an abuse risk.
I would be more comfortable if this admin interface only displayed (and retrieved from the server!) the entries that would be selected using a (non-null prefix?) search pattern.
Migrated from T4203 (view on Phabricator)