refactor(analytics): use flow.eligibility_verifier property instead

this is a more accurate value, and matches the internal EnrollmentEvent

benefits/core/analytics.py

@@ -45,7 +45,7 @@ def __init__(self, request, event_type, **kwargs):
         agency = session.agency(request)
         agency_name = agency.long_name if agency else None
         flow = session.flow(request)
-        verifier_name = flow.system_name if flow else None
+        verifier_name = flow.eligibility_verifier if flow else None
         enrollment_flows = [flow.system_name] if flow else None
 
         self.update_event_properties(