fix: simplify passing auditLog eventType (#15278)

Rename Trigger -> Event to be a more appropriate
name for the audit event.

Bonus: fixes a bug in AddMRFWorker() it did not
cancel the waitgroup, leading to waitgroup leaks.

cmd/object-api-datatypes.go

@@ -262,6 +262,7 @@ func (o ObjectInfo) tierStats() tierStats {
 type ReplicateObjectInfo struct {
 	ObjectInfo
 	OpType            replication.Type
+	EventType         string
 	RetryCount        uint32
 	ResetID           string
 	Dsc               ReplicateDecision