removed make_relation_node method from repository_node

include/matador/object/object.hpp

@@ -7,6 +7,7 @@
 #include "matador/utils/identifier.hpp"
 
 #include <list>
+#include <ostream>
 
 namespace matador::object {
 
@@ -38,6 +39,8 @@ public:
   [[nodiscard]] size_t constraint_count() const;
   [[nodiscard]] const std::list<class constraint>& constraints() const;
 
+  friend std::ostream& operator<<(std::ostream& os, const object& obj);
+
 private:
   friend class constraints_generator;
   friend class attribute_generator;