docs, conf, schemas: Add support for NVMe disks

docs, conf, schemas: Add support for NVMe disks

NVMe disks are essentially a namespace of an NVMe controller, but to
make it easier for the users to just add a disk, the necessary details
like adding the proper controller, setting the serial number for the
controller based on the disk, are done automatically.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Signed-off-by: Honglei Wang <honglei.wang@smartx.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>