CPU options for cloud-hypervisor

[jpds]

We need to expose a way for the user to add additional --cpus options at:

microvm.nix/lib/runners/cloud-hypervisor.nix

Line 96 in dfe2d3d

"--cpus" "boot=${toString vcpu}"

I tried to figure out a nice way to do this with Nix, but had to end with hard-coding it to make a machine work.

[astro]

I was not even aware cloud-hypervisor had that many CPU options!

To make it accessible from NixOS configuration, these hypervisor-specific bits can be exposed in hypervisor-specific NixOS options just like we already do for QEMU with microvm.qemu.extraArgs. They don't have to be as generic as extraArgs.

If you're ready to walk an extra mile with this, know that this project abstracts away specifics to present you with unified configuration of different hypervisors. It would take some time to research what capabilities can be controlled through common options.