Refactor validation for better readability

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

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

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

No files, tests, or entry points are identified. Start by locating handler registration and configuration parsing, then determine how handler monitoring should be exposed and how the new enable_monitoring option behaves. Done means monitoring is available for handlers while the option defaults to false.

Written by the indexing model from the issue text.