Add sys.addaudithook() and audit() (#3455)

Author: srittau

stdlib/3/sys.pyi

@@ -209,3 +209,5 @@ if sys.version_info >= (3, 8):
         err_msg: Optional[str]
         object: Optional[object]
     unraisablehook: Callable[[UnraisableHookArgs], Any]
+    def addaudithook(hook: Callable[[str, Tuple[Any, ...]], Any]) -> None: ...
+    def audit(__event: str, *args: Any) -> None: ...