PCI passthrough support

[DemiMarie]

This would allow passing PCI devices (attached over Thunderbolt) to a container. This includes, but is not limited to, external GPUs.

This is different than #62 because not all PCI devices are GPUs and the Apple iGPU is not a PCI device. While it is possible to expose some features of the iGPU to a VM, doing so is not “GPU passthrough” in the traditional sense.