Use Spack packages in in load_modules.sh
The current CI pipeline on DAS-5 will likely be migrated to DAS-6 in the coming months. DAS-6 doesn't have the schaap-stack
packages that are currently used here. DAS-5 now has a spack/9.3.0
module that provides modules for the same software (albeit different versions), we might want to try switching from schaap-stack
to Spack packages. If something breaks, we can extend/fix the Spack setup (on both clusters) before migrating.