MC event matcher

Adds a helper function to be able to iterate over DAQ/MC events easily.

Example:

julia> m = MCEventMatcher(f)
RBRIterator(ROOTFile{OnlineTree (11405 events, 11405 summaryslices), OfflineTree (11405 events)})

julia> @showprogress 1 for (event, mc_event) in m
            # ...
       end
Progress: 100%|███████████████████████████████████████████████████████████| Time: 0:00:21

added enhancement label

enabled an automatic merge when the pipeline for 4e488997 succeeds

merged

mentioned in commit 8caed419