[enhancement]: Disable cloud-init when packer is used to customize image

# Enhancement

Hello, we are working to implement cloud-init as a main provisionning instance tool on GCP.

Our custom company GCP image, could need to be be re-customized using packer as engine. we would like to be able to "disable" cloud-init when packer start à cloud-init based image.

But It look-like the actual mecanism available are is not suffisant to work with cloud and packer : https://cloudinit.readthedocs.io/en/latest/howto/disable_cloud_init.html