Update creating-a-new-detector.md to reflect current codebase

[JamieMagee]

Closes #1461

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.3%. Comparing base (b2822ac) to head (baabed1).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #1537    +/-   ##
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  Coverage   90.3%   90.3%            
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  Files        418     423     +5     
  Lines      35301   35608   +307     
  Branches    2187    2237    +50     
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+ Hits       31878   32168   +290     
- Misses      2981    2986     +5     
- Partials     442     454    +12     

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[Copilot]

Pull Request Overview

This PR updates the creating-a-new-detector.md documentation to reflect the current codebase structure and provide more comprehensive guidance for creating new detectors. The documentation has been significantly expanded from 155 lines to 415 lines with better organization, detailed code examples, and step-by-step instructions.

Key changes:

• Restructured content with clear sections for each step of detector creation
• Added detailed code examples for component types, detector classes, and unit tests
• Clarified detector lifecycle methods and maturity stages
• Improved explanations of graph construction and component registration
• Added practical guidance for running and debugging detectors