Interrogate spack.yaml/spack.lock via spack python rather than yq

[CodeGat]

During a meeting with upstream spack, it was noted that spack python can interrogate a lot of the information about the environment (spack.yaml/spack.lock) rather than yq.

This would lead to a more spack.yaml-independent method of getting package versions/metadata, which means the CD infrastructure doesn't need to be changed as much in response to spack.yaml changes.