Add new examples to binder-examples

[rgaiacs]

I was working in a minimal working example based on the Yuvi's JupyterCon 2025 talk "Not Just for Notebooks: JupyterHub in 2025" and I would like to contribute it to binder-examples:

• https://github.com/GESIS-Methods-Hub/minimal-example-flask
• https://github.com/GESIS-Methods-Hub/minimal-example-gui-bkchem

The README of both jupyter-server-proxy and jupyter-remote-desktop-proxy are great but I missed a minimal working example that I can navigate in less than 5 minutes and use as a template.