Figure out and document how to use devcontainer with GitHub codespace

I discovered that GitHub codespace also supports devcontainer.

https://github.com/nodejs/node/pull/60472#issuecomment-3467843933

This means for new Node.js contributors, they do not even need to download or install anything locally to start hacking on Node.js. Just click a few buttons on GitHub and they can start working on changes in the browser, and they can run tests in the container from the code space etc. as well. This might be very useful in code and learn sessions.

I don't know what extension codespace supports, but at least debugging the JS part of Node.js should be possible if the ports are set up correctly. One can always do command line debugging in the terminal in the code space as well. Or good old printing.

Codespace seems to be a paid feature but there's free tier available (?) so we'd be careful about directing people to it though

Start by reviewing the current devcontainer setup and the linked Node.js pull-request discussion about GitHub Codespaces. Document the steps for opening the project in a Codespace, running tests, and debugging, while clearly noting the available extensions and any paid or free-tier limitations.