This adds support for adding custom properties to the junit testcase element, based on the framework, requested in #153

This supports:

• NUnit.Category
• XUnit.Trait (either directly attached to a method or discovered via XUnit.TraitDiscoverer)
• Microsoft.VisualStudio.TestTools.UnitTesting.TestContext.TestProperty

Changes

Brief overview of the changes to areas of the project

GitHub actions

• Force color output for dotnet - that makes it easier to detect and read error messages in action logs
• Set up nuget cache using cache action (please note that with v4 this is natively integrated, I did not manage to set up v4 without too much fiddling with existing config)

If you are open for upgrading to v4 of the dotnet action I can also give it a spin, in a dedicated PR, please just let me know

Logger

• Extends junit xml serializer

Testing

• Created a new test (assets) project JUnit.Xml.TestLogger.XUnit.NetCore.Tests to verify the xUnit discoverer, also combined with traits works
• Create new test suite JUnitTestLoggerXUnitAcceptanceTests to run the added xUnit project
• Extended Junit.xsd schema & changes the inline format for changes to the file to make it easier to track down

Not entirely sure if thats the appropiate way to do for this repository, this way logic can be tested easily with xUnit