[qe-core][qem] Add check for unreleased container images
There is need to automate the release of 15-SP3 container images from https://build.suse.de/project/show/SUSE:SLE-15-SP3:Update:CR to https://build.suse.de/project/show/SUSE:SLE-15-SP3:Update:CR:ToTest.
Since 15-SP3 is not public, openQA container tests should not be scheduled and the container image should not be able to get released to the public registry.
This will be part of https://gitlab.suse.de/geor/container_bot.
Once this is implemented, the container_bot running in
qam.suse.de should have it's version updated.