As many times stated in this forum by the dev members, Docker support will never be added directly to Proxmox. Your best bet is to install Docker inside a LXC container (Now that nested containers are officially supported by Proxmox, that should be a fairly easy task to do, and you can even backup the container once you're done). If you're a GUI person like me you can always install "Portainer" and manage your Docker containers from there.