Add configuration options for serialization

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

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

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

No files or tests are named. Start by locating handler configuration and any existing serialization paths, then determine what handler serialization should cover and where enable_serialization is read. Done means the option defaults to false and clearly controls the requested serialization behavior, with tests covering both settings.

Written by the indexing model from the issue text.