I've been testing cockpit for months on my omv test VM. It doesn't seem to have any docker features that I can find. It is more for managing one or more machines. Maybe it has more features when running on redhat machines but it is pretty spares on Debian.
The link to the article shows how to set up dockers. Make Container Management Easy With Cockpit
It looks like you have been busy while I have be gone. Nice Work!