This diff introduces adding of the message object on message consuming from the Tunnelbroker client instead of the simple payload string.
To make these changes we are modifying the Tunnelbroker client integration in the Rust node addon adapter and adding a new flow type tunnelbrokerMessageToDeliver for the message.

Linear task: ENG-2615

1. The simple and easiest test is to check what message is consumed by adding a simple pub-sub to the keyserver/src/keyserver.js:

    import { getRustAPI } from 'rust-node-addon';
...
    const rustBinding = await getRustAPI();
    const tbClientBinding = rustBinding.TunnelbrokerClient;
    const tbClient = new tbClientBinding('ksDeviceID', (error, msg) => {
      console.log(`tbClient got message object:`);
      console.log(msg);
      if (error) {
        console.log(`tbClient got an error: ${error.toString()}`);
      }
    });
    tbClient.publish('ksDeviceID', 'Hello from keyserver');

2. Start the Tunnelbroker service: nix develop; cd services/tunnelbroker; cargo run.
3. Start the keyserver service: nix develop; cd keyserver; yarn dev.
4. The expected result should be the message object in the keyserver console which reflects the published message.