[cherry-pick] Update Basic configuration documentation

[nginx-bot]

Proposed changes

This commit changes the example YAML code block to single-source the contents from the actual GitHub code. It also updates some parts of the page structure to match contemporary style conventions.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-4.0@eef9326). Learn more about missing BASE report.

Additional details and impacted files

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##             release-4.0    #7586   +/-   ##
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  Hits                   ?    10771           
  Misses                 ?     9634           
  Partials               ?      431           

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