Add rate limiting for export

**Feature request**
It would be great to have import for core.

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

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

The title asks for export rate limiting, while the body asks for core import and an `enable_import` option, and no files, tests, or entry points are named. First clarify which feature is intended, then locate the configuration entry point and relevant tests; done should match the clarified behavior and preserve the stated default of `false` if import is confirmed.

Written by the indexing model from the issue text.