virtualisation: implement kubevirt config

KubeVirt[1] allows for VMs to be run and managed as pods inside of
Kubernetes clusters. Information about the guests can be exposed through
qemu-guest-agent[2] as well as startup scripts can be injected through
cloud-init[3].

This config has been duplicated and modified from the `cloudstack`
config/script.

To test this out, deploy KubeVirt locally with KinD[4], build the disk
image, then package it into a container image (or upload to CDI[5]) and
provision a VirtualMachine.

[1]: https://kubevirt.io/user-guide/
[2]: https://kubevirt.io/user-guide/virtual_machines/guest_agent_information/
[3]: https://kubevirt.io/user-guide/virtual_machines/startup_scripts/#cloud-init-examples
[4]: https://kubevirt.io/quickstart_kind/
[5]: https://kubevirt.io/user-guide/operations/containerized_data_importer/#containerized-data-importer

Signed-off-by: jbpratt <[e-mail]>

nixos/modules/virtualisation/kubevirt.nix

···
+{ config, lib, pkgs, ... }:
+
+{
+  imports = [
+    ../profiles/qemu-guest.nix
+  ];
+
+  config = {
+    fileSystems."/" = {
+      device = "/dev/disk/by-label/nixos";
+      fsType = "ext4";
+      autoResize = true;
+    };
+
+    boot.growPartition = true;
+    boot.kernelParams = [ "console=ttyS0" ];
+    boot.loader.grub.device = "/dev/vda";
+    boot.loader.timeout = 0;
+
+    services.qemuGuest.enable = true;
+    services.openssh.enable = true;
+    services.cloud-init.enable = true;
+    systemd.services."serial-getty@ttyS0".enable = true;
+
+    system.build.kubevirtImage = import ../../lib/make-disk-image.nix {
+      inherit lib config pkgs;
+      format = "qcow2";
+    };
+  };
+}