TauTrig offline Run3 monitoring : implement "mongroups" feature
This MR is going to implement "mongroups" feature on Run3 tau trigger monitoring following example from :
Logic is to extract the list of triggers to be monitored from json file encoding "mongroups" properties from trigger menu. If no "mongrups" properties are found, the trigger list will be taken from hard-coded list already present in the tau trigger monitoring code.