Allow log levels from lowercase

[toondaey]

Encountered this while testing and discovered that log levels can only be set with all caps. From experience, most users will usually prefer lower cases hence this change.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.47%. Comparing base (53274b6) to head (d97cbc5).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...te/extractorutils/unstable/configuration/models.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #482      +/-   ##
==========================================
- Coverage   80.51%   80.47%   -0.04%     
==========================================
  Files          43       43              
  Lines        4038     4046       +8     
==========================================
+ Hits         3251     3256       +5     
- Misses        787      790       +3     

Files with missing lines	Coverage Δ
...te/extractorutils/unstable/configuration/models.py	84.21% <87.50%> (+0.13%)	⬆️

... and 1 file with indirect coverage changes

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