start ack aggregator for thing twin modify commands and live messages

* If we'd start the aggregator for policy commands this will fail
  as the responses can't be transformed to an acknowledgement

Signed-off-by: Yannic Klem <yannic.klem@bosch.io>

internal/models/acks/src/main/java/org/eclipse/ditto/internal/models/acks/AcknowledgementAggregatorActorStarter.java

@@ -159,6 +159,7 @@ public static boolean shouldStartForIncoming(final Signal<?> signal) {
             result = !ackRequests.isEmpty();
         } else if (signal instanceof Command<?> command &&
                 Command.Category.isEntityModifyingCommand(command.getCategory()) &&
+                Command.isThingCommand(signal) &&
                 !isLiveSignal) {
             result = ackRequests.stream().anyMatch(AcknowledgementForwarderActorStarter::isNotLiveResponse);
         } else if (Command.isMessageCommand(signal) || isLiveSignal && Command.isThingCommand(signal)) {