feat: Add option to search for stubs packages

This allows using the feature in griffe that searches for stubs packages

Related: mkdocstrings/griffe#221

src/mkdocstrings_handlers/python/handler.py

@@ -61,6 +61,7 @@ class PythonHandler(BaseHandler):
     fallback_config: ClassVar[dict] = {"fallback": True}
     """The configuration used to collect item during autorefs fallback."""
     default_config: ClassVar[dict] = {
+        "find_stubs_package": False,
         "docstring_style": "google",
         "docstring_options": {},
         "show_symbol_type_heading": False,
@@ -110,6 +111,7 @@ class PythonHandler(BaseHandler):
     """Default handler configuration.
 
     Attributes: General options:
+        find_stubs_package (bool): Whether to load stubs package (package-stubs) when extracting docstrings
         allow_inspection (bool): Whether to allow inspecting modules when visiting them is not possible. Default: `True`.
         show_bases (bool): Show the base classes of a class. Default: `True`.
         show_source (bool): Show the source code of this object. Default: `True`.
@@ -279,7 +281,7 @@ def collect(self, identifier: str, config: Mapping[str, Any]) -> CollectorItem:
             try:
                 for pre_loaded_module in final_config.get("preload_modules") or []:
                     if pre_loaded_module not in self._modules_collection:
-                        loader.load(pre_loaded_module)
+                        loader.load(pre_loaded_module, find_stubs_package=final_config["find_stubs_package"])
                 loader.load(module_name)
             except ImportError as error:
                 raise CollectionError(str(error)) from error