add option to use spack upstream repos

conf/common/build.yml

examples/01_real-from-ideal.sh

platforms/common/spack_utils.sh

templates/common/build_icon.sh

templates/common/build_python_environment.sh

templates/common/run_icon.sh

templates/real-from-dwd-ana/prepare_experiment.sh

templates/real-from-ideal/prepare_experiment.sh

templates/real-from-ideal/run_ideal.sh