Improve error messages in validation

**Feature request**
It would be great to have search for models.

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

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

Locate the configuration parser and the model-selection or search entry point; no file or test is named in the issue. Done means an `enable_search` option defaults to false and model search is available when enabled, with tests covering both settings.

Written by the indexing model from the issue text.