[add-on] no flush with org.apache.deltaspike.jpa.api.transaction.Transactional #readOnly and hibernate

jpa supports FlushModeType COMMIT and AUTO. for some use-cases that isn't enough. in case of org.apache.deltaspike.jpa.api.transaction.Transactional#readOnly(true) you will get a #rollback instead of a #commit at the end of the transaction. however, with some other frameworks you can get special behavior. e.g. some use org.hibernate.FlushMode#MANUAL once they detect hibernate as the jpa-provider. deltaspike only provides portable features and therefore you won't get such a special behavior out-of-the-box. however, deltaspike provides a rich set of extension-points. with a custom org.apache.deltaspike.jpa.spi.transaction.TransactionStrategy it's a matter of less than 100 loc to integrate org.hibernate.FlushMode#MANUAL as mentioned above. you can find a corresponding prototype here.