Requiring leptons to pass primary triggers for MET Trigger monitoring plots

Before all HLT_electrons/muons were used for the MET monitoring plots where at least one 'signal' lepton was required. This is susceptible to changes in our plots from changes in leptons which we'd like to be insensitive to.

Now only the HLT_electrons/muons passing the primary chains: HLT_e(26|28)_lhtight_ivarloose_L1.* HLT_mu24_ivarmedium_L1.* are used for the MET monitoring plots, which should remain more stable for our use.