code: def _register_config_file(self, key, val):
          
          state = self.__load_state()
          if 'config_files' not in state:
              state['config_files'] = {}
          state['config_files'][key] = val
          self.__dump_state(state)
docs: Persist a newly added config file, or update (overwrite) the value
          of a previously persisted config.