[report-service] Implement DB row item type
Summary:
This diff implements a struct that represents a row in the database. Also implemented conversions from/to attribute maps and other helper traits.
Depends on D8938
Test Plan: Tested later in the stack.
Reviewers: michal, patryk, varun, jon
Reviewed By: jon
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D8939