Installs a default configuration file into the active store.
Provide a generalised method to save a default configuration object for an already enabled module or theme as part of an update from Drupal 7 to Drupal 8's configuration management system.
string $type: The extension type; e.g., 'module' or 'theme'.
string $config_name: The configuration object name to retrieve.
boolean True on success, false if config file does not exist.
function update_7_to_8_install_default_config($type, $config_name) {
  // Build the new configuration object.
  $config = Drupal::config($config_name);
  // Extract the extension namespace/owner from the configuration object name.
  $name = strtok($config_name, '.');
  // Load and set default configuration values.
  $file = new FileStorage(drupal_get_path($type, $name) . '/config');
  if (!$file
    ->exists($config_name)) {
    return FALSE;
  }
  // Apply and save the default values.
  $config
    ->setData($file
    ->read($config_name))
    ->save();
  return TRUE;
}