Allow for adding upstream data via Git submodule
In data/MIMOC_cf, there is an example of a Git submodule providing upstream data. Implement a renderer for this case.
A replacement for the old instance build runner (old tags dind/docker-in-docker) is available. For details see https://git.geomar.de/open-source/gitlab-docu/-/wikis/build_runner
In data/MIMOC_cf, there is an example of a Git submodule providing upstream data. Implement a renderer for this case.