Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/profiles/standard/standard.profile

@@ -0,0 +1,27 @@
+<?php
+/**
+ * @file
+ * Enables modules and site configuration for a standard site installation.
+ */
+
+use Drupal\contact\Entity\ContactForm;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Implements hook_form_FORM_ID_alter() for install_configure_form().
+ *
+ * Allows the profile to alter the site configuration form.
+ */
+function standard_form_install_configure_form_alter(&$form, FormStateInterface $form_state) {
+  // Add a placeholder as example that one can choose an arbitrary site name.
+  $form['site_information']['site_name']['#attributes']['placeholder'] = t('My site');
+  $form['#submit'][] = 'standard_form_install_configure_submit';
+}
+
+/**
+ * Submission handler to sync the contact.form.feedback recipient.
+ */
+function standard_form_install_configure_submit($form, FormStateInterface $form_state) {
+  $site_mail = $form_state->getValue('site_mail');
+  ContactForm::load('feedback')->setRecipients([$site_mail])->trustData()->save();
+}