[services] Extract common database code to a separate lib
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