DataImportCron only support registry source

[Muyan0828]

Is your feature request related to a problem? Please describe:
we want to create DataImportCron with other sources, such as http and s3.

[awels]

The problem with other sources is that there is no standard way to identify new images. With container registry it is possible to compare digests and determine if the image in the registry is different. For other sources there is no such standard and thus really hard to identify if something changed.

We had an attempt before:
#2881

We still want this just haven't had the time to really investigate and complete it.