Abstract project cloner configuration as a configuration setting for admins

Similar to Abstract editor configuration as a configuratio... (#396418) but for the project cloner configuration

See also related thread to extract values to be configurable (e.g. via ENV vars): !125358 (comment 1469663627)

There isn't a requirement to allow this to be configured at instance/gorup/subgroup level. The only requirement so far is that it the organizations can choose which image to use while cloning the projects in the workspace. Thus the work in Allow editor and project cloner images and tags... (#438767 - closed) should suffice?