Annotation to declare a Pojo-Entity as graph backed relationship entity.
It is used by the Neo4jRelationshipBacking aspect to add field advices as well as the RelationshipBacked interface.
Relationship entities cannot be instantiated directly. The will be provided by relationship fields and the
methods relatedTo and getRelationshipTo introduced to the node entities.
the relationship-type of this entity will be used if no other type is provided, either as field inside
the relationship-entity or via an annotation in the node-entity, this type will take precedence over node-entity #