[services] Backup - add Database Entities Tools

Summary:
There is a "DB schema" described as in D2950 and the method for creating items by type.

Depends on D3076

Test Plan: -

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/D3081