docs: enable private docstring members sphinx (#28586)

docs/api_reference/create_api_rst.py

@@ -80,6 +80,8 @@ def _load_module_members(module_path: str, namespace: str) -> ModuleMembers:
             continue
         if type_.__module__ != module_path:
             continue
+        if ":private:" in (type_.__doc__ or ""):
+            continue
 
         if inspect.isclass(type_):
             # The type of the class is used to select a template