fix: add back integration usage stats

Created by: dadlerj

Fixes https://github.com/sourcegraph/sourcegraph/issues/3893

Tested on sgdev (https://sourcegraph.sgdev.org/site-admin/usage-statistics):

I haven't worked in browser extension code for at least 6 months now... Please help me verify there aren't any edge cases I'm potentially missing here! Looks like this handles Phabricator as well as all browser extensions, but would love your take