Method to read configuration from testconfig.json

[nicholass-alcidion]

It would be highly useful for us to have a mechanims to read configuration from the testconfig.json

Previously in xunit we would use .runsettings and specify <RunSettings><RunConfiguration><EnvironmentVariables> and then read these envrionment at test time. This was used for example to know what database server(s) to connect to.

Given that Microsoft.Testing.Platform makes use of testconfig.json (and envrionment varialbes) in a method similar to Microsoft.Extensions.Configuration - it would be useful to have a way to use this to read custom configuration properties.

I am hoping for something similar to TestContext.Configuration.Get("config:property:path");