[Refactor] Producent

[Augustyn]

Class com.example.javaopencommerce.producer.Producer and it's usage (from DTO to DBA) should be refactored in the same way as ex. Order.

[pawelKapl]

I think that the most obvious example would be also Item or Image. The key is to keep it totally separated from other domain models, accesible via QueryRepository (CQRS) for Reading, and by Facade for modifying, no other access points. Producer knows about item only via producer id on item