[DX] Add a helper function for messaging after saving settings forms

I find myself having to look up the string The configuration options have been saved. quite often. Can we add a helper function that does a backdrop_set_message with this string for us?

function backdrop_add_config_saved_message() {
  backdrop_set_message(t('The configuration options have been saved.));
}

We could update core to use this function wherever we currently hard-code the string