Feature/1018 update unit test project layout

[hocinehacherouf]

Description

What's new?

• Resolve Feature: Unit tests of each dotnet project should be placed on a dedicated folder #1018
• Resolve Feature: Migrate dotnet sdk to 6.0.400 #1059

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Tests
• Other

[codecov]

Codecov Report

Merging #1042 (c94d1cb) into main (abf776a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1042   +/-   ##
=======================================
  Coverage   85.45%   85.45%           
=======================================
  Files         179      179           
  Lines        5859     5859           
=======================================
  Hits         5007     5007           
  Misses        852      852           

Impacted Files	Coverage Δ
.../AzureIoTHub.Portal/Server/Helpers/ConfigHelper.cs	86.99% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.