Details is an object generated for each image, containing
it's created_at date to properly set response headers. It
also can be expanding in the future to include an image's
dimensions, which we can expose via an API endpoint.
In addition to this, Details allows us the ability to
re-generate processed images. For now, all images which
do not yet have an associated Details will be
re-generated upon access. Details is set for each
thumbnail on generation, so this will only happen once
for each image.
