Support for Acquia DAM Assets

I created a PR to call a hook that allow get the FID on AcquiaDAM Assets fields

example for a referenced Media that have a field named as field_acquiadam_asset_document referencing Acquia DAM Assets

/**
 * Implements hook_search_api_attachments_get_fid().
 */
function example_module_search_api_attachments_get_fid(MediaInterface $media) {
  if ($media->hasField('field_acquiadam_asset_document')) {
    return $media->get('field_acquiadam_asset_document')->target_id;
  }
  return NULL;
}

I attach a patch in case referencing gitlab causes issues.