[services] Backup - add Database Manager base

Summary:
Base/inner functions for the database manager. This diff may be beneficial for this task https://linear.app/comm/issue/ENG-324/avoid-repetitions-in-services-code because this is the mutual code that may be put in a separate place.

Depends on D3081

Test Plan:

cd services
yarn run-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/D3082