update grouping default to new lockfile mechanism

[wilsonmr]

Blocked by NNPDF/reportengine#41

Using the redux to apply default grouping. Added some tests to make sure it works as intended - these will of course fail until that PR is merged (unless you have dev install of reportengine)

cc: @siranipour

[wilsonmr]

I don't foresee any issues but I want to run a comp fits report on this branch just to make sure.

[wilsonmr]

I've removed the mapping here for the default grouping because in the end this is a fallback default which I don't think we need more than one value for. Originally we wanted to potentially allow for a different default for, say, theory covariance reports however the point is that specifying that you want a different default in this case is just as much effort (and more confusing) that explicitly stating the grouping you want or using the fixed grouping production rules (i.e produce_group_dataset_inputs_by_process)

[siranipour]

Do we reckon there is much left in NNPDF/reportengine#41

[wilsonmr]

I think the point is to check that this looks ok and maybe at least make a template for dataset defaults to see how that will work before merging that - side note I also need to fix the tests there.

I thought I should at least minimally do this part.

[siranipour]

Just rebasing this onto master to build on it in another PR

[scarlehoff]

Closing this since NNPDF/reportengine#41 has been stale for more than two years now :(