[DOC] - Add link to keycloak docs for root management

[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

See Original discussion

The idea is to have only root as the administrator of keycloak, and we advise the user to change the password. But all this is out of the scope of installation and deployment, this point is addressed in the Keycloak docs of Nebari (I linked the current ones).

Steps to Resolve this Issue

add link + explanation

[viniciusdc]

blocked by #93

[kcpevey]

This is now unblocked since #93 is merged.