[services] Tests - Add dummy tests

Summary:
Depends on D4249

Added the rust files for tests where they're supposed to be placed. For now, hardcoded throwing unimplemented but it's supposed to be replaced with tests' logic.

Test Plan: none for now

Reviewers: palys-swm, varun

Reviewed By: palys-swm, varun

Subscribers: ashoat, palys-swm, Adrian, atul, yayabosh

Differential Revision: https://phab.comm.dev/D4250