Filters for custom State Providers missing

[KDederichs]

At the top of the Filters page it states:

You can also add filtering support to your custom [state providers](https://api-platform.com/docs/core/state-providers/) by implementing interfaces provided by the library.

Sadly neither the Filters page nor the State Providers Page mentions what those Interfaces are and how to use them. It'd be nice if that could be added to the docs.

[Ardenexal]

This would be very helpful for us. We have separated our doctrine from API resources to maintain DDD and this requires setting up custom filters as it won't work with the default doctrine ones. Some examples of how to use filters when not connected directly to an ORM or ODM would be very useful