Improve default machine type selection

If an explicit machine type is not specified in the VM config, the qemu driver will select the first machine type in the list of machine types for the specified accelerator. See virQEMUCapsGetPreferredMachine https://gitlab.com/libvirt/libvirt/-/blob/master/src/qemu/qemu_capabiliti... On my test machines, this works reasonably well for x86_64 where the first machine type is pc-i440fx-7.1. But for aarch64, the first machine is integratorcp, which is not very useful with maxCpus=1 and other limitations. Would it be possible to select a "better" default machine type? E.g. 'pc' for x86_64, 'virt' for aarch64, etc. I'm happy to work on this if folks deem it's a reasonable improvement. It would benefit tools like the libvirt terraform provider, which prefer to use something more generic like <type>hvm</type>. Regards, Jim