[RF] Add support to set the nominal value and limits for the ShapeFactor parameters in HistFactory

[TomasDado]

Explain what you would like to see improved and how.

Currently, the code allows to pass the nominal value and the limits for the NormFactors via:

void RooStats::HistFactory::Sample::AddNormFactor	(	std::string const &	Name,
double	Val,
double	Low,
double	High )

But there is no similar function for ShapeFactors, only:

void RooStats::HistFactory::Sample::AddShapeFactor	(	std::string	Name	)	

is available. This has the disadvantage that in some cases the limits hardcoded in the code might be very sub-optimal resulting in convergence issues.

Please note, the ShapeFactors are important e.g. for ABCD esimate, see page 23 here (and replace NormFactor with ShapeFactor): https://cds.cern.ch/record/1456844/files/CERN-OPEN-2012-016.pdf

ROOT version

any

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Operating system

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