Add TypeScript types for helpers

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

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

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

The issue names no files, tests, or entry points. First reconcile the TypeScript-helper title with the serialization request, then locate the configuration handling and helper definitions; done means the intended TypeScript types and the stated serialization option are implemented and covered by the relevant existing checks.

Written by the indexing model from the issue text.