This diff introduces the get_nonce_to_sign internal function which is a gRPC unary request to the Tunnelbroker server to obtain a nonce string to be signed. The function gets the pointer to the Tonic client and deviceID and returns the nonce from the server to be signed with the sign_string_with_private_key function from D5999.
This function also introduced a native_rust_library/src/tunnelbroker_client.rs file which will contain a requests functions.
Linear task: ENG-2434