Merge config with radiuss-spack-config one

[adrienbernede]

This is an attempt to merge the spack configuration with radiuss-spack-config one.

If this work out well, we should submit the change to radiuss-spack-config, and ultimately use it as a submodule to provide the configuration.

2 limitations:

• at the beginning of the packages config, there are permission and provider sections, we may want to place them in the spack.yaml.
• at the end on the packages config, there are all the external utilities we do not rebuild. We should decide if we want to keep those or not.