(FM-7693) Add Windows Server 2019
(FM-7693) Add Windows Server 2019

The DSC module now supports Windows Server 2019.  This commit
updates the metadata.json to show that Server 2019 is supported.

jpogran/puppetlabs-dsc,puppetlabs/puppetlabs-dsc,puppetlabs/puppetlabs-dsc,jpogran/puppetlabs-dsc,jpogran/puppetlabs-dsc,puppetlabs/puppetlabs-dsc