[DOC] - Expand nebari-config examples for GPU, Node selectors, and more, for each cloud provider

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

Occasionally, we find ourselves needing a sample at hand or pointing to some part of our documentation that details and exemplifies the uses and customizations in the configuration. For example, what is the correct structure for adding a GPU to a JupyterLab profile? Which provider uses which node selector, etc.

We need to update our documentation to include step-by-step guides and examples that cover the essentials of configuration customization, including GPU integration and the use of node selectors across different providers, as well as how exactly they should be used, scenarios, etc.

This would also ease the onboarding process for new users trying out Nebari by giving them a clearer understanding of our configuration usage. Occasionally

• #427
• #428
• #425

Steps to Resolve this Issue

1. Clarifications on the correct structures for GPU additions and insights into provider-specific node selectors

Start by reviewing the existing nebari-config documentation and the linked issues #427, #428, and #425 to identify the remaining examples. Document step-by-step GPU and provider-specific node-selector configurations, including when to use them across each cloud provider. Done means the essential structures, scenarios, and provider differences are covered with usable examples.