[services][blob] Add reverse index database methods
Summary:
Implemented methods for managing the blob-service-reverse-index table. They will be needed in subsequent diffs. This is mostly the same approach as in D5693 (parent diff).
Part of ENG-2300
Depends on D5693
Test Plan: Called these locally and ensured that entities are properly inserted/queried/removed from database.
Reviewers: varun, jon, tomek, marcin
Reviewed By: varun
Subscribers: ashoat, atul
Differential Revision: https://phab.comm.dev/D5694