Added a guide on howto test custom quirks in zha

[Hedda]

Proposed change

Added a guide for how-to add a custom zha quirk for testing.

Additional information

This is a compliment to the guide for writting quirks -> #4349

Device diagnostics

Not applicable for this context.

Checklist

• The changes are tested and work correctly
• pre-commit checks pass / the code has been formatted using Black
• Tests have been added to verify that the new code works
• Device diagnostics data has been attached

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.13%. Comparing base (2e2bbd9) to head (bc42364).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #4355   +/-   ##
=======================================
  Coverage   92.13%   92.13%           
=======================================
  Files         358      358           
  Lines       11919    11919           
=======================================
  Hits        10981    10981           
  Misses        938      938           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.