[services] Tests - Add tools

Summary:
Depends on D4164

Adding tools with one function: generate_nbytes. It returns n bytes (that are the same).

Test Plan: this doesn't do anything on its own. Tests can be built.

Reviewers: palys-swm, geekbrother, varun

Reviewed By: palys-swm, varun

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

Differential Revision: https://phab.comm.dev/D4225