New Gaudi feature: use StaticHistograms where applicable

• StaticHistograms are strictly what Histograms were before Gaudiv39
• the new (Gaudi v39) histograms allows to define title/axis/labels/... at initialization time, avoiding the hassle of the std::optional we were using before (and doing strictly that inside actually)

So ideally one should use StaticHistogram when everything is known at compile time.

@sponce