Add SSO integration tests

[VMelnalksnis]

Resolves #113.

Changes proposed in this pull request:

• Add SSO tests using containerized keycloak (Dev environment setup #15, Add Docker support #205)

[codecov]

Codecov Report

Merging #427 (25d87cc) into master (5620627) will increase coverage by 1.56%.
The diff coverage is 59.01%.

@@            Coverage Diff             @@
##           master     #427      +/-   ##
==========================================
+ Coverage   64.54%   66.10%   +1.56%     
==========================================
  Files         258      259       +1     
  Lines        6836     6854      +18     
  Branches      532      533       +1     
==========================================
+ Hits         4412     4531     +119     
+ Misses       2262     2152     -110     
- Partials      162      171       +9     

Impacted Files	Coverage Δ
...hade.Avalonia.Core/Authentication/SystemBrowser.cs	0.00% <0.00%> (ø)
...meshade.Avalonia.Core/Configuration/OidcOptions.cs	42.85% <0.00%> (-17.15%)	⬇️
...Gnomeshade.Avalonia.Core/Authentication/Browser.cs	61.81% <61.81%> (ø)
...omeshade.WebApi/Configuration/AuthConfiguration.cs	100.00% <100.00%> (+28.00%)	⬆️
...ource/Gnomeshade.WebApi.Client/GnomeshadeClient.cs	79.52% <0.00%> (+2.36%)	⬆️
...ebApi/V1_0/Authorization/ApplicationUserHandler.cs	86.95% <0.00%> (+8.69%)	⬆️
.../Gnomeshade.WebApi/HealthChecks/OidcHealthCheck.cs	55.55% <0.00%> (+22.22%)	⬆️
...Gnomeshade.WebApi.Client/TokenDelegatingHandler.cs	65.00% <0.00%> (+65.00%)	⬆️
...Authentication/ExternalAuthenticationController.cs	69.44% <0.00%> (+69.44%)	⬆️
... and 2 more

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