[DOC] - Add an example for running lumen apps

[aktech]

Preliminary Checks

• [X] This issue is not a question, feature request, RFC, or anything other than a bug report. Please post those things in GitHub Discussions: https://github.com/nebari-dev/nebari/discussions

Summary

Lumen is a cool agent based framework for chatting with data and for retrieval augmented generation (RAG): https://github.com/holoviz/lumen

It would be great to add an example in the documentation on how to run a lumen app.

lumen.command.ai serve {--}port={port} {--}disable-index-redirect {--}allow-websocket-origin=example.com --ip=0.0.0.0 --ready-check-path=/ready-check --ready-timeout=120