[DOC] - Review current docs on how to use and configure jupyter-galery

[viniciusdc]

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

After #528 was merged, a few questions from its initial review round remained open that required further inspection in the overall text and documentation. This issue is a reminder to review and follow up on the current merged instructions about Jupyter Gallery and also improve any gaps that might now exist.