Add Docker auth to CircleCI

[jtniehof]

Docker is limiting anonymous pulls from the Docker hub (more). This is done by IP so basically all CircleCI users are lumped together. The recommended way around this is to add Docker Auth to the CircleCI setup so at least we're limited based on an individual user account rather than being all lumped together. This is going to require figuring out how to get the secrets injected into CircleCI without putting them into the repository.

CircleCI conversation

Closure condition

Pipeline config updated, any new accounts created and this whole process documented.