A good model for how easy integration should be from an author's perspective would be something like Sentry (example integration docs).
Perhaps what's needed could be described as "Sentry for feature usage metrics"?
In fact, although Sentry is primarily aimed at error aggregation, it seems very close to being a good fit for this: perhaps it can be extended to allow for good feature usage reporting and metrics, too?
(If not, it can at least serve as design inspiration.)