How to use provided interfaces for configuration?

In a few places the documentation references interfaces that can be used to implement new classes to provide alternative behavior to release-please. One such part of the documentation is: https://github.com/googleapis/release-please/blob/main/docs/customizing.md#adding-additional-versioning-strategy-types

If I implement a new strategy/class using these interfaces, where would that code need to be written so that release-please can find the implementation at runtime and use it? I suspect that this documentation is not describing how you can contribute back to release-please but more-so how you can extend it. Is that correct or are these interface intended to be used to contribute back to release-please itself?