Saving tau decay mode inside PFTau and patTau

Fixing long standing issue when decay mode was not saved in PFTaus and it was not possible to recalculate it on-the-fly (it depends on nChargedHadrons and nPiZeros which are only transient). The decay mode is now saved also in patTau. Although the data member existed in pat::Tau before, it was not filled by default. Now it is filled during construction from the PFTau.

The RECO event size is increased by this PR, but the increase is very small. The top estimate is ~100b/event which I got for workflow 25202. The relative size increase was 0.5-1.0E-4 depending on the density of the event

@monicava, @veelken