Add rate limiting for export

**Feature request**
It would be great to have backup for middleware.

**Use case**
Many users need this functionality for production deployments.

**Implementation idea**
Add a new config option `enable_backup` with default `false`.

The issue names no files, tests, or entry points. Start by locating the middleware, export, and configuration handling, then determine how the requested rate limiting relates to the proposed `enable_backup` option; done means the intended behavior and default-false configuration are implemented and verified.

Written by the indexing model from the issue text.