Addition of DAOD_SUSY21 for compressed EWK SUSY analysis
SUSY21 targets Z->1e+1gamma+low-pT electron track events for low-pT electron track tagger calibration, which will be used for compressed EWK SUSY analysis. The skimming requires 1 electron with pT>30 GeV, 1 gamma with ET>30 GeV, and their invariant mass to be > 50 GeV.