This diff introduces the implementation of `NewSession` gRPC handler using the Rust Tonic gRPC server by calling the `newSessionHandler` C++ handler wrapper function.
The new implementation is a wrapper of the [[ https://github.com/CommE2E/comm/blob/378c4da22d309b11cb6695c277569e86ae7dd172/services/tunnelbroker/src/Service/TunnelbrokerServiceImpl.cpp#L68-L129 | current NewSession C++ handler ]] for using and calling from Rust gRPC server codebase.
Linear task: [[ https://linear.app/comm/issue/ENG-2059/implement-tunnelbroker-grpc-newsession-api-handler-in-rust | ENG-2059 ]]