Add Windows Hyperv support

[jsturtevant]

Add the correct fields to the spec at https://github.com/containerd/nerdctl/blob/f316402913c4239a2388b7467bcffc9735dd8327/cmd/nerdctl/run_windows.go#L42

Something like:

isolation := cmd.Flags().GetString("isolation")
if isolation == "hyperv" {
	opts = append(opts, oci.WithWindowsHyperV)
}

See https://docs.docker.com/engine/reference/commandline/run/#specify-isolation-technology-for-container---isolation

[dcantah]

Planning to look at this next week