improve imagepuller configuration experience / imagepuller docs missing traefik and project-clone

See lengthy discussion in CRW-3429 and https://docs.google.com/drawings/d/1y0DjF-NcDQ-LsR-9XsgTLRs9fCm13uTieA4hJY6a96Q/edit ... several plans have evolved from the discussion, so I've moved the work to a new issue so we can resolve CRW-3429 and continue the planning here.

Three options are:

• Deprecation of checluster option
• Customization via bash script (https://github.com/redhat-developer/devspaces-demo) or `chectl server:imagelist` (new feature) to fetch image list for configuring imagepuller
• Crontab for OOTB config, but using smaller container image like KIP itself - https://gist.github.com/amisevsk/9df020a46156b1824cd71a45785449aa

It is likely that we may decide to do 2 or more of these as they solve different customer/user needs.