[ATR-20361] Update skeleton.RDOtoRDOtrigger.py to be able to read the legacy L1 XML
Update skeleton.RDOtoRDOtrigger.py to be able to read the legacy L1 XML for components which still require access to these data via the TrigConfSvc.
I tested this as part of !26071 (merged) but a) this is not directly related and b) it shouldn't have to wait for that big MR. Hence this MR is being submitted from the GitLab UI.
This is temporary code to continue to support Run2 algs while the migrate over to Run3 trig configuration.