Redirect contact form on submit
Here is what I ended up doing in a custom module if anyone else needs to do this


use Drupal\Core\Url;

function custom_module_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {

  //contact page form
  if ($form_id == 'contact_message_feedback_form') {
    $form['actions']['submit']['#submit'][] = 'custom_module_contact_submit';
    dpm($form['actions']['submit']);
  }

}

function custom_module_contact_submit(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
    drupal_set_message('we sent a form woohoo');
    $url = Url::fromRoute('contact.site_page');
    $form_state->setRedirectUrl($url);
}