NSM Wiki: Add unique user counter for wiki page and design views with Usage Ping
Also track the number of unique users viewing wiki pages, in addition to creates/updates/deletes which are already tracked.
It looks like this is currently implemented in
lib/gitlab/usage_data_counters/track_unique_events.rb, which gets called automatically for all events that create an
Event record. We don't do that for page views, so we can probably just manually increase the counter at https://gitlab.com/gitlab-org/gitlab/-/blob/8b272bb8fddbfa23460bab54787f513eaddff8bf/app/controllers/concerns/wiki_actions.rb#L70.