Implement Barlow-Beeston for partially analytic profiling

[lukasheinrich]

Description

the profiling across the gammas can be analytically solved

https://github.com/root-project/root/blob/4fa59f4fb80fd914cb84144e5218e55397810c01/roofit/histfactory/inc/RooStats/HistFactory/RooBarlowBeestonLL.h

https://github.com/root-project/root/blob/4cac5a12f98eebc39e9b9888ab6b11b40cddf09d/roofit/histfactory/src/HistFactorySimultaneous.cxx#L127

[lukasheinrich]

https://arxiv.org/pdf/1103.0354.pdf