[services] Extract common database code to a separate lib

Summary:
Create a new lib where all the common database code for Rust services can be placed.

Depends on D6853

Test Plan: Compile and run blob and backup services. Still have to check how it affects Docker builds.

Reviewers: michal, bartek, jon, varun

Reviewed By: bartek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6854