Add branch name in dumux-docker-ci to image name
The names of images generated in dumux-docker-ci now include the name of the branch they were generated from (dumux-docker-ci#14, dumux-docker-ci!44). DuMux pipelines pass it through to the triggered lecture pipeline (dumux!3799 (merged)) by the variable DUMUX_DOCKER_CI_BRANCH
, which can also be set when manually starting a pipeline.