Consider deprecating old models API

**Feature request**
It would be great to have filtering for handlers.

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

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

Start by locating the handler configuration and existing configuration options in the repository. Clarify how handler filtering should work and where `enable_filtering` is read; the change is done when the option defaults to `false` and filtering behavior is covered for production deployments.

Written by the indexing model from the issue text.