Add FreeBSD support as qemu-images
This is modelled after the other templates with the exception that the BSD images are only available as QEMU images, not as normal containers. Other than that the behavior should be the same as our existing templates.
The inspiration came from wayland/wayland!146 (closed), @emersion's work made it obvious what needed to be done here (fsvo of "obvious" anyway).
Note: need to set up at least one real-world use-case before we can merge this
Edited by Peter Hutterer