Add support for multiple webhooks

[StefH]

No description provided.

[codecov]

Codecov Report

Merging #615 (00ae055) into master (93ab4e1) will decrease coverage by 0.06%.
The diff coverage is 84.40%.

@@            Coverage Diff             @@
##           master     #615      +/-   ##
==========================================
- Coverage   75.91%   75.84%   -0.07%     
==========================================
  Files         148      148              
  Lines        5693     5710      +17     
  Branches      578      582       +4     
==========================================
+ Hits         4322     4331       +9     
- Misses       1193     1199       +6     
- Partials      178      180       +2     

Impacted Files	Coverage Δ
src/WireMock.Net/Models/Webhook.cs	100.00% <ø> (ø)
src/WireMock.Net/Server/WireMockServer.Admin.cs	55.66% <0.00%> (-0.45%)	⬇️
src/WireMock.Net/Owin/WireMockMiddleware.cs	90.56% <66.66%> (+0.18%)	⬆️
src/WireMock.Net/Server/RespondWithAProvider.cs	92.30% <91.02%> (+0.07%)	⬆️
...ck.Net.Abstractions/Admin/Mappings/MappingModel.cs	100.00% <100.00%> (ø)
src/WireMock.Net/Mapping.cs	98.18% <100.00%> (ø)
src/WireMock.Net/Serialization/MappingConverter.cs	58.19% <100.00%> (+1.72%)	⬆️
src/WireMock.Net/Serialization/WebhookMapper.cs	78.57% <0.00%> (-4.29%)	⬇️

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[StefH]

#614