Function config_set 

pub fn config_set(
    store: &LocalFsStore,
    flags: &OpFlags,
    payload: Option<UpdateConfigSetPayload>,
) -> Result<OpOutcome, OpError>

op updates config-set — set the update-channel notification policy. Only the fields supplied are changed; the rest keep their stored value. An absent update-channel.json is seeded from disabled (deny-by-default), so the first config-set is what turns the channel on.