How to use cloud-init with a debian-based image on Google Cloud?

How to use cloud-init with a debian-based image on Google Cloud?

cloud-init is installed on the latest (at the moment of writing) Ubuntu 18.04 LTS (ubuntu-1804-bionic-v20191002) image :

<my_user>@instance-1:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.3 LTS"

<my_user>@instance-1:~$ which cloud-init
/usr/bin/cloud-init