Add pre-processing script.
Similar to what the post-processing does, allow for adding pre-processing steps.
This would catch #8 (closed) by providing a way of injecting the code necessary for adding Git submodules.
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
Similar to what the post-processing does, allow for adding pre-processing steps.
This would catch #8 (closed) by providing a way of injecting the code necessary for adding Git submodules.