[Feature]: Support Windows Nano Server

Is your proposal related to a problem?

Hi, I downloaded OVA file (vmware vm) of WIndows Server 2016 Nano. the file is 180MB only! and it unpacks to 4GB disk. I think it would be fantastic case for dockur, to run minimalistic windows environment. Can you support it natively, to choose it as a version in ENV and pull it automatically?

Describe the solution you'd like.

If the answer is no, or meanwhile; Is there a way for me to test it, like dry run it. i have converted that vmdk from ova to raw img disk, and I'm trying to trick dockur into running it, but he is too smart for me, and always detects the disk is not previous dockur installation so it just moves it to /backup/unknown and starts downloading some iso to setup a new disk from scratch. Can I specify something like VERSION: "custom" and just let dockur try to run the container as is, to see what happens.

thanks in advance!

Describe alternatives you've considered.

the only other way I can try for now is to try to run directly kvm/qemu vm...

Additional context

No response