Optimize server start up time

[kabilar]

Thanks @aranega for this suggestion.

It takes several minutes to pull the Docker images from Docker Hub when starting up a pod.

To reduce the server start up time, could we host a private registry with the Docker images on AWS in the same zone as the k8s cluster? These Docker images could be synced with the images on Docker Hub.

cc @vijayiyer05

[asmacdo]

We could host a private registry, however, that might be heavier than we need. Jupyterhub config allows us to prepull the images.

https://z2jh.jupyter.org/en/stable/administrator/optimization.html#pulling-images-before-users-arrive