[services] Move common files from tests to src
Summary:
As discussed in comments here, this diff moves helper files from tests to src.
Depends on D5171
Test Plan: cargo build and cargo test --no-run and check if it compiles
Reviewers: tomek, varun, jon, inka
Reviewed By: tomek, jon
Subscribers: ashoat, atul, karol, abosh
Differential Revision: https://phab.comm.dev/D5189