use existing encode_json to avoid code duplication, rename queryset customization param and move it to Meta, move docs to models from inheritance

ormar/__init__.py

@@ -25,12 +25,12 @@ except ImportError:  # pragma: no cover
     from importlib_metadata import version  # type: ignore
 from ormar.protocols import QuerySetProtocol, RelationProtocol  # noqa: I100
 from ormar.decorators import (  # noqa: I100
+    post_bulk_update,
     post_delete,
     post_relation_add,
     post_relation_remove,
     post_save,
     post_update,
-    post_bulk_update,
     pre_delete,
     pre_relation_add,
     pre_relation_remove,