Changes to GET /api/v3/submissions/:id/files

added the optional property issues/items/reason to the response with the 400 status

added the optional property issues/items/reason to the response with the 401 status

added the optional property issues/items/reason to the response with the 403 status

added the optional property issues/items/reason to the response with the 404 status

added the optional property issues/items/reason to the response with the 410 status

added the optional property issues/items/reason to the response with the 429 status

added the optional property issues/items/reason to the response with the 500 status

added the optional property issues/items/reason to the response with the 503 status

endpoint added