(PDB-1072) Add endpoint to mirror report command structure.

This commit adds an endpoint called event-reports, the return value of which
can be easily munged for resubmission as a report. In an HA context, this will
allow us to transfer reports from one database to another over HTTP without
needing a second query for the events associated with a report.
need to think about whether we have better options than this pattern. The issue is limit/offset on API responses that comprise multiple rows.