Bonus Docker Task: Push image to registry

[SashaWeinstein]

I was really impressed by Jae's data challenge where he pushed an image to docker registry with his solution to the docker/SQL tasks. This is quite advanced and definitely shouldn't be required, but maybe we could add it as a bonus.

Even if someone doesn't actually get the image to the registry, I would like to see that they know what that means and have a plan to do it.