Specialization of LocalSessionFactoryBean which registers a "group_concat" hsl function for any known dialect.
Note : I would have inlined this class in #sessionFactory() if I could. But Spring enhances RepositoryConfig in
a way that the product of #sessionFactory() is expected to have a null-arg constructor. Yet, the default
constructor of an inner / anonymous class is a 1-param ctor which receives the outer instance. This leads to
arcane reflection errors (NoSuchMethodException "There is no no-arg ctor") in lines that seem completely unrelated