Generate cloud-init/Ignition configs

[korewaChino]

Let odorobo generate sidecar images for cloud images to mount and fetch cloud-init configs from

[korewaChino]

Actually we might be able to just set the serial number in Cloud Hypervisor

  "platform": {
    "serial_number": "ds=nocloud,.."
  },

Just tested, works when using EDK2