Add a TODO for options_by_section

Author: Pierre-Sassoulas

pylint/config/arguments_provider.py

@@ -162,6 +162,9 @@ def options_by_section(
 
         (section, [list of (optname, optdict, optvalue)])
         """
+        # TODO 3.0: Make this function private see
+        # https://github.com/PyCQA/pylint/pull/6665#discussion_r880143229
+        # It's only used in '_get_global_options_documentation'
         warnings.warn(
             "options_by_section has been deprecated. It will be removed "
             "in a future release.",