Test => Add software package dependencies for BrainScaleS(-2)… [WIP]

This initial commit simply tries to build most of the BrainScaleS-2 software dependencies. For the full "thing" we would need:

• spack download cache for source packages (as download sources sometimes change),
• maybe a spack build cache for faster builds,
• some of our environment creation code (→ via spack views),
• probably remove the duplication and directly use our singularity-based flow upstream (requires changes on our side) .