This diff introduces a `publish` class method for the napi-rs bridge Tunnelbroker client class.
It uses a client-shared function from the D6284 to push a message to the `mspc` which is bound to the gRPC tx stream.
Linear task: [[ https://linear.app/comm/issue/ENG-2729/implement-napi-rs-bridge-in-keyserver-for-the-tunnelbroker-shared | ENG-2729 ]]