Update Javadoc for @Data

[sergvasylchak]

The javadoc on Data.java says it generates a constructor, which is the equivalent of @RequiredArgsConstructor behavior. In reality though, the constructor is only generated if no explicitly defined constructors (including explicit Lombok constructors) already exist. The behavior is expected and documented here.

The javadoc alone, however, often causes confusions, since there is no clear explanation on why the constructor in @Data may or may not be generated, which leads to a need of additional digging in Lombok documentation.