Allow setting Content-Length header on the response

[StefH]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 92.40506% with 12 lines in your changes missing coverage. Please review.

Project coverage is 86.58%. Comparing base (7e162a0) to head (e72a2bc).
Report is 1 commits behind head on master.

Files	Patch %	Lines
....Net.Tests/Owin/Mappers/OwinResponseMapperTests.cs	91.80%	0 Missing and 10 partials ⚠️
...rc/WireMock.Net/Owin/Mappers/OwinResponseMapper.cs	92.30%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1158      +/-   ##
==========================================
+ Coverage   86.57%   86.58%   +0.01%     
==========================================
  Files         426      426              
  Lines       23939    23961      +22     
==========================================
+ Hits        20724    20746      +22     
  Misses       2314     2314              
  Partials      901      901              

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