Change includeSubscriptionEventType to Set<SubscriptionEventType> in Subscription
According to the ONE Record API spec v2.0.0, includeSubscriptionEventType is a Collection of SubscriptionEventType see https://github.com/IATA-Cargo/ONE-Record/blob/master/working_draft/API/ONE-Record-API-Ontology.ttl#L1065
The current implementation, expects includeSubscriptionEventType to be optional string. see https://git.openlogisticsfoundation.org/wg-digitalaircargo/ne-one/-/blob/bba8c3f87d6a7d6ace279d991cf7ed32530614b9/src/main/java/org/openlogisticsfoundation/neone/model/Subscription.java#L27
Introduction of SubscriptionEventType (enum) analogous to NotificationEventType (enum)