services/postgresql: Use functions as defaults instead of mutable types

docs/services/postgresql.rst

@@ -39,6 +39,7 @@ Define tables
 -  In PostgreSQL, use ``TEXT`` instead of other character types, as there is `no performance difference <https://www.postgresql.org/docs/current/datatype-character.html>`__.
 -  Use ``NOT NULL`` with character types, `as recommended by Django <https://docs.djangoproject.com/en/4.2/ref/models/fields/#null>`__.
 -  Use ``NOT NULL`` with JSON types, and set the default to an empty object, array or string.
+-  In Python, do not set default values to ``{}`` or ``[]``. In Django, use ``default=dict`` and ``default=list``. In Pydantic (including SQLModel), use ``default_factory=dict`` and ``default_factory=list``.
 
 .. seealso::