tauRec: add a neural network based tau decay mode classifier

Prescription

A neural network based tau decay mode classifier is added in tauRecTools package. This algorithm is appended to the tool list in tauRec to be executed. The DeepSet neural network based classification result and the probability for the tau to be classified as each decay mode are decorated to the TauJet. Names of the variables are NNDecayMode, NNDecayModeProb_[1p0n,1p1n,1pXn,3p0n,3pXn]. The study is presented in those slides.

The neural network weights file, i.e. the configuration file for lwtnn graph, can be set as a flag in tauRec, currently the weight file is /cvmfs/atlas.cern.ch/repo/sw/database/GroupData/tauRecTools/00-02-00/NNDecayModeWeights-20200625.json

lwtnn info

• atlasexternals!693 (merged) has been merged.

tagging @xiaozhon , @adbailey , @gipezzul , @martindl , @cgrefe for reviewing