[services] Tunnelbroker - Adding of Tonic crate to cargo dependencies

Summary:
This diff introduces adding the Tonic to cargo dependencies for the Rust library in Tunnelbroker.
The purpose of adding Tonic is to use it for gRPC communication.

Related Linear task: ENG-1072

Test Plan: No test plan, this is just a dependency.

Reviewers: jon, tomek, varun

Reviewed By: jon, tomek

Subscribers: ashoat, tomek, atul, abosh

Differential Revision: https://phab.comm.dev/D5265