Update homepage

[pavithraes]

Preliminary Checks

• 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

Nebari homepage (https://www.nebari.dev) content was authored ~2 years ago. Nebari has changed and improved significantly since hence, and we should update the messaging accordingly.

Steps to Resolve this Issue

Non-exhaustive list of improvements:

1. Add more details about "what" Nebari is, i.e., mention JupyterHub more clearly
2. Cover [DOC] - Explain some Nebari concepts and use cases #323
3. Re-visit "why choose nebari" -- clearly note environment management
4. Remove jitsi from integrations list
5. Update the GIF to use new JHub Apps launcher
6. Mention extensibility (plugin mechanism)
7. In the deployment options, add bare metal and other supported options
8. TBD