[DOC] - Updates pages that mention JHub Apps Launcher

[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

JHub Apps has a new UI and a new docs site: https://jhub-apps.nebari.dev. Nebari docs need to be updated to indicate these.

Steps to Resolve this Issue

The following pages need to be updated:

• https://www.nebari.dev/docs/how-tos/jhub-app-launcher
• https://www.nebari.dev/docs/tutorials/create-dashboard (link to jhub apps docs, instead of duplicating instructions, whenever possible, to maintain a single source of truth)
• https://www.nebari.dev/docs/tutorials/login-keycloak -- screenshots need updating

Also, add a link to JHub Apps docs in the top navbar