Changes to List files accessible to the authenticated user

added ExternalMetadataResponse subschema #2 to the results/items/external_metadata response property oneOf list for the response status 200

added the media type application/json for the response with the status 401

added the media type application/json for the response with the status 403

added the media type application/json for the response with the status 404

added the media type application/json for the response with the status 429

added the non-success response with the status 503

removed ExternalMetadataResponse from the results/items/external_metadata response property allOf list for the response status 200

added the required property results/items/pending_reprocess to the response with the 200 status

added the required property results/items/thumbnail to the response with the 200 status