Move workflow from direct sourcing of `setup-env.sh` to spack module

[CodeGat]

See #367

Background

We are moving away from directly sourcing $spack/share/spack/setup-env.sh and instead using modules.

Instead of sourcing this file, use the new modules:

module use /g/data/vk83(/prerelease)?/modules
module load spack/1.1

This would deprecate the .github/actions/get-deploy-paths action in build-cd as we would be able to get all the relevant information from spack itself - for example:

# spack location
spack location --spack-root
# spack deployment location
realpath $(spack location --spack-root)/..
# spack-config location
realpath $(spack location --spack-root)/../spack-config
# spack environment (specific)
realpath $(spack location --spack-root/../environments/$SOME_SPACK_ENV