Enable log level filtering on the TimelineLogAdmin page

[swrichards]

The log level is actually included in our timeline logger, although (mostly) the level defaults to INFO: that's something I'd like to start changing in future, but for now, we can actually already filter on logging level without adding a special flag, by using Postgres JSON field lookup functionality.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 58.82353% with 7 lines in your changes missing coverage. Please review.

Project coverage is 94.57%. Comparing base (df9656f) to head (2f8ee05).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/open_inwoner/utils/admin.py	58.82%	7 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1445      +/-   ##
===========================================
- Coverage    94.58%   94.57%   -0.01%     
===========================================
  Files         1069     1071       +2     
  Lines        39623    39720      +97     
===========================================
+ Hits         37478    37566      +88     
- Misses        2145     2154       +9     

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