Add the capability to fetch and run public container images (Docker Hub, AWS,...)

[sfabbro]

Running public container images could be made possible on the CANFAR science platform.

• Users may be interested in sharing publicly their containers
• More familiar and possible easier tooling around Docker Hub or other
• Many large scientific collaborations maintain a set of container images (i.e. Euclid, Rubin,...)

Somewhat a duplicate of #398 but also more general.

[shinybrar]

+1 for this issue, currently harbor is a big detriment to our development efforts for the following reasons,

1. Upload from Github CI often fail to Harbor, mid-upload.
2. The labelling of images on Harbor is cumbersome.
3. we cannot use the same image to spawn a jupyterlab session or headless, since we cannot have more than 1 label on an image
4. Because, at the launch of each job, in the job description itself we specify the kind of job, the label architecture is redundant.

[ijiraq]

Relates to bug in #448