Fix bug in method makeAsimovDataValerio

Release notes

This fix aims at fixing the bug in creating Asimov dataset with mode "valerio". A small amount of changes and documentation are added to the action "MakeAsimovDataset".

Details

Instead of loading nominal snapshots after running unconditional fit to observed data, we should save the NPs and Global observables to separate snapshots and use them to fit to this Asimov later.