Track why mentions didn't happen
Track why mentions didn't happen

Right now we don't actually know how many times
each of these cases happen so add some basic tracking
so we can make some informed decisions.

Bug: T135719
Change-Id: Id4d519aefe96ecca2e3c51dd1c8128de70d0caac

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo