Add support for automated RHEL images
This commit allows for a completely automated release cycle of upstream RHEL images
Images are downloaded from RedHat via the RHSM using an offline api token, though this step is only performed if an existing PROD image with the RHEL timestamp does not currently exist in OpenStack.
Once a new image is downloaded, the image is converted for use on the CERN cloud and tests are performed via image-ci
If running via a scheduled pipeline (and should the tests pass), the image is shared with CERN RHEL users and an email is sent to these users to inform them