support existing certificate for xRDCertificateConfiguration via Thumbprint

[ghost]

It looks like the Set-RDCertificate cmdlet has a -Thumbprint option that lets you use a existing certificate in the localmachine\my environment. However, i don't think this is supported in the DSC version yet.

It would be great if we where able to use this feature. That way we can install the certificate from a kv directly onto our local store in the vm and configure rds with it