Websocket demo

[oplatek]

Thanks to Jindra Vodrazka for all the help setting this app.

Jindra set it up I just plan it/ask Jindra to do it, and test it out and summarize here in the PR.

[martinpopel]

Thanks @oplatek. Before merging, please consider fixing the high-severity vulnerabilities discovered by Dependabot (by updating werkzeug==2.2.2 to Werkzeug>=3.0.3 and flask>=2.2.5 and testing if it works, I guess).

[oplatek]

Shoot. Last week, Dependabbot was appeased by updating the flask to 2.2.5 (or I thought it was). Will do.

[oplatek]

@martinpopel fixed and tested.

Btw can we add the apache license? #2