[services-lib] Make DB attribute names non-static

Summary: Similiar to D8627 but in comm-services-lib. The difference is that I used impl Into<String> to add some flexibility

Test Plan:
Following bash one-liner:

cd services
for r in "comm-services-lib" "backup" "blob" "feature-flags"; do pushd $r; cargo check --all-features; popd; done

Reviewers: michal, jon, varun

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8787