Creates the extension setting for a list of Feed Items.

  Args:
    client: an AdWordsClient instance.
    feed_items: the list of all Feed Items.
    campaign_feed: the original Campaign Feed.
    feed_item_ids: the Ids of the feed items for which extension settings should
        be created.
    platform_restrictions: an optional Platform Restriction for the Feed items.

def CreateExtensionSetting(client, feed_items, campaign_feed, feed_item_ids,
                           platform_restrictions=None):
  """Creates the extension setting for a list of Feed Items.

  Args:
    client: an AdWordsClient instance.
    feed_items: the list of all Feed Items.
    campaign_feed: the original Campaign Feed.
    feed_item_ids: the Ids of the feed items for which extension settings should
        be created.
    platform_restrictions: an optional Platform Restriction for the Feed items.
  """
  campaign_extension_setting_service = client.GetService(
      'CampaignExtensionSettingService', 'v201809')

  extension_feed_items = [{
      CreateSitelinkFeedItem(feed_items, feed_item_id)
  } for feed_item_id in feed_item_ids]

  extension_setting = {
      'extensions': extension_feed_items
  }

  if platform_restrictions:
    extension_setting['platformRestrictions'] = platform_restrictions

  campaign_extension_setting = {
      'campaignId': campaign_feed['campaignId'],
      'extensionType': 'SITELINK',
      'extensionSetting': extension_setting
  }

  operation = {
      'operand': campaign_extension_setting,
      'operator': 'ADD'
  }

  campaign_extension_setting_service.mutate([operation])