Test-DscConfiguration as part of PR checks

[brianwest]

There is currently no test to validate that a DSC configuration, including each DSC resource updated as part of a PR, generates a useable MOF file, before merging.

I'd like to add a test to the Azure Pipeline, which will ensure that a MOF file generated by a DSC configuration, consisting of each resource being touched by a PR, is tested using Test-DscConfiguration.

MOF files could be manually tested, but that's more time consuming and error prone.

This is to prevent situations where a DSC resource does not produce a working MOF file, despite passing the existing tests.