[services] Backup - Add DB operations for Logs

Summary:
Database operations for LogItems

Depends on D3161

Test Plan: Backup service still builds

Reviewers: palys-swm, geekbrother, varun, ashoat, jimpo

Reviewed By: palys-swm, ashoat

Subscribers: benschac, ashoat, palys-swm, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D3175