Add settings.worker.config-image field

MR is adding settings.worker.config-image field alongside settings.worker.image field which will allow overriding citool-config used in a TF request. Same as worker image, it is validated against a regex and allowed for admins only.

Relates to RFD3 - Testing Farm Release Process.

Related MRs: infrastructure!1306 (merged), ranch-public!11, cli!218 (merged)

Part of TFT-4503.