Improved error message from the GET /menus endpoint when the Amazon™ S3 service is unavailable

Previously, if the Amazon S3 service was unavailable, the GET /menus endpoint of the menus API would return a 404 HTTP error code with the message:

No published data found for restaurant GUID: [restaurant-guid]. Make sure restaurant GUID is correct and that data has been published.

This message was misleading because it provided the wrong cause and resolution for the problem.

Now, when the Amazon S3 service is unavailable, the GET /menus endpoint returns a 503 HTTP error code with the following message:

Unable to retrieve menus for restaurant due to a service outage.