[DOC] - Environment configuration page has missing link

[kcpevey]

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

There is a link to a non-existent page for creating dashboards on the docs/explanations/advanced-env-configuration.md page. Here is the quote:

`nebari-git-nebari-git-dashboard` to [create shareable dashboard][create-dashboards].

Steps to Resolve this Issue

Point to existing docs or correct the link path.