Trigger efficiency

[katilp]

(from #7 - @slaurila )

If we can find an existing measurement for the trigger efficiency of HLT_IsoMu17_eta2p1_LooseIsoPFTau20 for data and MC, would it make sense to publish it in the Open Data portal e.g. as a json file? Then it would be very straightforward to apply the trigger efficiency scale factors in the analysis (again, could be done by @anniinakinnunen starting from the json). Alternatively, we should come up with a tag-and-probe example for measuring the trigger efficiency, which then moves this item to the "longer-term" list.