notification queue limit has no maxLimit (#9380)

New value defaults to 100K events by default,
but users can tune this value upto any value
they seem necessary.

* increase the limit to maxint64 while validating

pkg/event/target/mqtt.go

@@ -99,9 +99,6 @@ func (m MQTTArgs) Validate() error {
 			return errors.New("qos should be set to 1 or 2 if queueDir is set")
 		}
 	}
-	if m.QueueLimit > 10000 {
-		return errors.New("queueLimit should not exceed 10000")
-	}
 
 	return nil
 }