Support for more precise specification of disk drives

Even though QEMU supports it, the UI of UTM allows not to specifiy details.

e.g. IDE drives are created in this sequence:
IDE0.0
IDE0.1
IDE1.0
IDE1.1

but in reality, each of these four allow for two drives, a master and a slave; which is why QEMU has the index command.

So there could be:
IDE0.0 index 0
IDE0.0 index 1
IDE0.1 index 0
IDE0.1 index 1
IDE1.0 index 0
IDE1.0 index 1
IDE1.1 index 0
IDE1.1 index 1

This is particularly relevant, as CD-ROM drives are created as
IDE0.1
as this is the MS-Windows standard. But some legacy operating systems, in particularly NeXTSTEP and OpenStep, which as predecessors of macOS/i(Pad)OS would be particularly interesting to run on a Mac or iOS device, expect the CD-ROM drive to be at:

IDE0.0 index 1

it is thus impossible to install these operating systems under UTM.

Similar issues are applicable in regards to SCSI, where it’s impossible to indicate target and LUN (logical unit number). Again, certain legacy operating systems expect certain devices to be accessible under a specific target and LUN, and UTM simply sequentially allocating them, all with LUN0, isn’t allowing this to work.