egammaMVASvc: Enhance photon conversion handling and add flag resolution

In this MR we update the configuration of the egamma MC MVA calibration, in particular the configuration of Reconstruction/egamma/egammaMVACalib/Root/egammaMVASvc.cxx

No change is expected in the output.

This is needed since in the new calibration for Run3 we are going to deploy we have a different definition of converted photons. egammaMVASvc already have a flag to handle it, which by default is false (=old definition).

We want to avoid switching this flag to true based on geometry or other properties which identify Run3. The definition of conversion is now encoded inside the ROOT files the service (actually the tools inside it) is using. These ROOT files encode the weights of the MVA calibration, so it is the best way to store the definition of converted photons used during the training. So the service now tries to look for it and configure itself accordingly. If the property is not found inside the ROOT file then the default behaviour (old conversion definition) is used. In this way, old calibration will continue to work. The property has now a default value -1 which means that the tool will try to autoconfigure it. Any other value will overwrite the configuration.

Component accumulator used in reconstruction is updated. ElectronPhotonFourMomentumCorrectionTool, used at analysis level, is also updated.

The configuration has been tested in four different conditions: (old ROOT files without the new information / new ROOT files with the new information) x (property set manually / property not set manually).

@linghua @gunal @kristin @ahabouel @mungo @fnechans @christos @lnasella @bpascual