Merge request report widget instrumentation fixes

Problem to Solve

Our instrumentation implementation requires the existence of both known events and a metrics definition in order for service ping to accept the incoming data and report appropriately.

When !89078 (merged) was implemented, the event names are all generated dynamically and so there is no attachment of known_events and metric definitions.

Proposal

We need to create the initial set of known_events and metric definitions for the currently existing widgets. We should also update documentation that any new widgets need to make sure to include those files.