Revert "Remove unused kwargs in Api.definition decorator"

This reverts commit 0ed8a5b.

Those kwargs can be used when not calling definition in decoration mode:

api.definition('Pet')(PetSchema, extra_fields={'x-field': 'value'})

flask_rest_api/__init__.py

@@ -102,11 +102,11 @@ def definition(self, name):
                 class PetSchema(Schema):
                     ...
         """
-        def decorator(schema_cls):
+        def decorator(schema_cls, **kwargs):
             if APISPEC_VERSION_MAJOR < 1:
-                self.spec.definition(name, schema=schema_cls)
+                self.spec.definition(name, schema=schema_cls, **kwargs)
             else:
-                self.spec.components.schema(name, schema=schema_cls)
+                self.spec.components.schema(name, schema=schema_cls, **kwargs)
             return schema_cls
         return decorator