Add xunit report paths in products UI

[andrei-epure-sonarsource]

To be consistent with what we currently have

Repro steps:

1. Open a project in SonarCloud/SonarQube
2. Go to Administration -> General Settings -> Languages
3. Choose C#

Expected: NUnit , VsTest and xunit paths are mentioned.
Actual: Only NUnit and VsTest report paths are mentioned.

[andrei-epure-sonarsource]

@tom-howlett-sonarsource does it make sense at all to have coverage report paths in the SQ UI?