[native/rust_library] Adding of the Tunnelbroker Tonic client initialization

Summary:
This diff introduces adding the Tonic client initialization function for the Tunnelbroker into the Rust native library. The client instance would be passed to the client functions following the current approach.

Linear task: ENG-1333

Test Plan: The native apps are successfully built.

Reviewers: varun, jon

Reviewed By: varun

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5997