Add local testing/debugging CometD server setup guidance

What's missing in the repo is a way to test the code against a local CometD server/host. Preferable Dockerized. Do you have experience on that when developing this lib?
I noted to potential starting points:
- https://github.com/cometd/cometd-nodejs-server (NodeJS based)
- https://github.com/cometd/cometd/tree/5.0.x/cometd-demo (JAVA based)
If you can provide guidance, please share!