feat: add utility tool to validate histogram contents against a reference

[eguiraud]

A reference file for the configuration with N_FILES_MAX_PER_SAMPLE=1 is provided as well.

The tool:

• compares histogram edges and contents against a JSON reference file
• can also dump the contents of the histograms as json in order to produce new reference files
• ignores mismatches in the contents (but not the edges) of histograms with name containing "pt_res_up", because the content of these histograms depends on a random number generator
• only considers the highest namecycle in case there are multiple cycles for the same histogram (e.g. name;1 and name;2)

Fixes #136 .

[alexander-held]

Thanks! This is going to be very helpful. Given that we'll want to add more references for different settings and also will pick up some new systematics that will cause histograms to change, could you perhaps also add a script example for the JSON reference generation?

[eguiraud]

That would be just python validate_histograms.py --dump-json (assuming the input has the default file name histograms.root, otherwise you also pass that to the --histos option).

Is that what you mean? I'm not sure where to put that other than the --help as it's now?

[alexander-held]

Perfect, I hadn't looked closely enough at the code yet. No need to change anything then!

[ekauffma]

Can we add a description of this tool to the README for cms-open-data-ttbar?

[eguiraud]

@ekauffma sure, done!