Defaults for datasets

Created by: siranipour

Let's you do stuff like

dataset_defaults_spec: 40

dataset_inputs:
- {dataset: ATLASDY2D8TEV}
- {dataset: LHCB_Z_13TEV_DIELECTRON}

theoryid: 53

use_cuts: internal

template_text: |
  {@groups_covmat@}

actions_:
- report(main=True)

And it will apply the cfac, sys etc. as per the NNPDF40_nnlo_as_0118 runcard