Implement configurable module loading

We want to make it configurable, which module implementation is used. Once this is available, we can remove the `with...`-methods in `PlatformBuilder` and migrate the setup of the `TurtleGossipModule`.

Start by tracing module selection through PlatformBuilder and locating how TurtleGossipModule is currently set up. Determine the intended configuration mechanism and the scope of replacing the `with...` methods; the work is done when module implementations can be selected configurably and the stated migration is complete.

Written by the indexing model from the issue text.