Build RHEL8 images on Openshift Cluster

Development for a new pipeline that builds RHEL8 images on cluster instead of the existing server.

The build time on the existing RHEL8 builder pipeline is usually 30-40min. I expect the new pipeline to execute everything in 10-15 min (maybe a bit more), similar to the Ubuntu builder pipeline. In other words, this work will speed up the RAN-Container-Parent by 15min.

The physim python code has been updated to expect the physim images directly on the image registry.

Tasks to be done:

• Add to Gitlab Jenkinsfile: https://jenkins-oai.eurecom.fr/view/RAN/job/RAN-RHEL8-Cluster-Image-Builder/
• Need to check whether it is faster to build the target images (gNB, eNB, ...) serially and not in parallel
• it seems the Pipeline does not pick up the XML file @defosseu could you please check? -> I used the wrong branch/need to have the pipeline clone ci-build-cluster branch into Jenkins workspace