[WebSocket] Fix chat demo to updated TLS function.

[Faless]

Old cert + key/servername have been replaced with the new TLSOption configuration object.

The scene changes are just the result of opening the project and re-saving the scene with godot 4.0.2 stable.

[Faless]

Needs cherry pick to the 4.0 brannch.

[Faless]

Let me know if you prefer I split the scene and GDScript changes.

[mhilbrunner]

Note that here is already https://github.com/godotengine/godot-demo-projects/pull/909