Handle edge cases in caching

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

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

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

No files or tests are named. Start by locating the configuration handling and route-import code, then trace how the new enable_import option would affect route loading. Done means the option defaults to false and the requested route import works when explicitly enabled.

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