chore: deduplicate logging and clean up config

[jennifer-richards]

The only functional change here is preventing double log entries on 5xx requests. This was happening because the django.request logger had its own handler attached. As refactored here, 4xx errors (warnings) are discarded by the "level" filter in the django.request logger, and the actual log is emitted after propagating up to the django logger.

Along with the above, reformats the LOGGING code using ruff style and removes old comments that are more confusing than helpful at this point. Removes the Django 1.x method of suppressing admin mail for SuspiciousOperation errors. Instead, configures the django.security logger to be console-only and not to propagate.

Adds status_code to the JSON log. This is only relevant for django.request logs, where it will normally be 500. Other logs will have a null value.

Beware a little bit of churn in the commits...

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.36%. Comparing base (76fd25a) to head (7b30a77).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10592      +/-   ##
==========================================
- Coverage   88.36%   88.36%   -0.01%     
==========================================
  Files         327      327              
  Lines       44092    44120      +28     
==========================================
+ Hits        38964    38987      +23     
- Misses       5128     5133       +5     

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