Add ElectronTruthDecoratorAlg

Similar to !58959 (merged), !51948 (merged) this merge request adds an algorithm that decorates electrons with truth information. Three variables are added.

• ftag_truthOriginLabel is an integer origin defined here.
• ftag_truthVertexIndex is an integer label for the truth vertex from which the electron track originated. A value of 0 is reserved for the truth PV, while other truth vertices in the event are indexed arbitrarily after sorting the tracks according to their pT. Truth vertices within a configurable distance (by default set to 0.1mm) are merged.
• ftag_truthTypeLabel, which is a signed truth type label for each electron origin

    Other    = 0,
    Pion     = 1,
    Kaon     = 2,
    Electron = 3,
    Muon     = 4,
    PhotonConv = 5

Both algorithms (TrackTruthDecoratorAlg and SoftElectronTruthDecoratorAlg) could use some functions from TrackTruthDecoratorAlg and they were moved to a separate file to avoid code duplication.

Also, I added the same prefixes (ftag_) to all decorators from the previous MR (!58959 (merged))

@fdibello @svanstro @dguest