Fixup: Pin all repos used

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!50

Fix build of pynn-brainscales@ebrains_release-1-rc2

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!49

that is currently installed at CSCS

abstracted some more variables and simplified the process
of adding a new site

Fix py-torch build (maybe)

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!48

adds LFPy@2.2.3

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!47

Fix py-torch build

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!46

PyTorch 1.9.1 (fixed in versions >= 1.10.0) depends on an older onnx
version that utilizes a deprecated function from Google's protobuf
library that was removed in version 3.18.0 (see
https://github.com/protocolbuffers/protobuf/pull/8794/).

Workaround by specifying an explicit version range for this
dependency.

Readd pynn-brainscales (new version)

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!43

Re add pynn brainscales

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!42

Readd py-torch with onnx_ml disabled

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!41

Adding Snudda package.py

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!40