session and insert query builder progress

include/matador/utils/primary_key_attribute.hpp

@@ -48,6 +48,7 @@ private:
 };
 
 const primary_key_attribute DefaultPkAttributes {};
+const primary_key_attribute Identity {generator_type::Identity};
 const primary_key_attribute ManualVarChar63 {63};
 const primary_key_attribute ManualVarChar127 {127};
 const primary_key_attribute ManualVarChar255 {255};