Update "Try" page to use JupyterLab 4

[JasonWeill]

The "Try" page links to JupyterLite demos, based on JupyterLab 3. We should offer a way to try JupyterLab 4 in browser, preferably not using Binder at this time, to save on our Binder capacity.

[ivanov]

Thanks for this report, @JasonWeill, not sure when this happened, but it currently uses @jupyterlab/application v4.0.7 so going to go ahead and close this one.
Happy hacking!