Add the updated field to those that should be indexed in mongo.
Add the updated field to those that should be indexed in mongo.

When we find annotations, we default to sorting by most recently
updated.  This needs an index when there are enough annotations.

DigitalSlideArchive/large_image,girder/large_image,DigitalSlideArchive/large_image,girder/large_image,girder/large_image,DigitalSlideArchive/large_image