For now, as S2I and Runtime image tags, we can only specify the full image tag, like for example registry/namespace/builder-name:version

Sometimes, the build images are already present into the internal Openshift registry and we should leverage the reuse of the internal image, because specifying the whole internal image won't work as the internal certificate is not verified ... like image-registry.openshift-image-registry.svc:5000/openshift/kogito-quarkus-jvm-ubi8-nightly:temp-master-tests