Outbox Event Router SMT can move type to header only if renamed eventType

The Outbox Event Router SMT offers custom placement of the outbox pattern table fields based on `table.fields.additional.placement`.

Because of the following test and logic in EventRouterConfigDefinition.java:

if (EventRouter.ENVELOPE_EVENT_TYPE.equals(addField.getAlias())) {
  eventTypeMappingProvided = true;
}
// ....
if (!eventTypeMappingProvided) {
	additionalFields.add(0, new AdditionalField(AdditionalFieldPlacement.ENVELOPE, eventTypeColumn, EventRouter.ENVELOPE_EVENT_TYPE));
}

I believe the header placement of field `type` is only possible if and only if it's renamed `eventType` (except if duplicating the configuration as such `"type:header:eventType,type:header"` which in turn set two headers instead of one).

I am not sure of the reason of this logic at all but it prevents people from having `type` as header with its original name (without duplicating the field).