Add configuration to log user in request finished to support DRF auth

[jrobichaud]

Closes #37

[codecov]

Codecov Report

Merging #38 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #38   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           40        40           
  Lines          940      1008   +68     
=========================================
+ Hits           940      1008   +68     

Impacted Files	Coverage Δ
django_structlog/middlewares/request.py	100.00% <100.00%> (ø)
test_app/tests/middlewares/test_request.py	100.00% <100.00%> (ø)

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