[Mercure][Feature] Configure automatic mercure updates

As far as I can see, API Platform sends updates on insert/update/delete (`\ApiPlatform\Core\Bridge\Doctrine\EventListener\PublishMercureUpdatesListener::onFlush`) automatically. This causes performance problems if many entities are updated/inserted/deleted at once. In my case, I'm not listening to inserts and deletions, so it doesn't make sense to send the updates in the first place.

It would be great if some kind of configuration would be possible.