[service] Move services lib to shared
Summary: Part of ENG-5555 -> in order to move the backup client from commtest to shared (to use it from native) we need to move the comm_services_lib to shared, because the client uses e.g. the UserIdentity struct. It would be good to have a common library for all Rust code in our codebase anyway. This diff also renames the library to comm_lib as it will stop being used only for services.
Test Plan: Find-and-replace comm_services_lib with comm_lib. Test if all services build.
Reviewers: bartek, varun, kamil
Reviewed By: bartek
Subscribers: wyilio, ashoat, tomek
Differential Revision: https://phab.comm.dev/D10256