Add configuration options for caching

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

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

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

No file or test is named in the issue. Start by locating the configuration handling and the code that discovers or searches handlers; verify the new enable_search option defaults to false and that enabling it makes handler search available, with existing tests passing.

Written by the indexing model from the issue text.