Integration tests for management scripts

Currently, the plethora of bash scripts orchestrating the ingestion pipeline are completely untested. We would like to have basic integration tests that run the full pipeline on a single, small test repository. This test should be run for both "local" mode and Slurm mode, and ideally in CI. This requires

• a Docker image with all backend dependencies,
• ... + a Slurm installation for the Slurm mode tests,
• integration in the future CI workflow (see !35 (merged)).

I propose to build the Docker image using Nix and its dockerTools for reproducibility and perfect match with the development environments defined in the various Nix shells in the repository.