[Doc] Plugin API usage

[eddiebergman]

There's no way to know what inputs I'm meant to give to a Plugin as documented here: https://automl.github.io/DeepCAVE/main/examples/api/parallel_coordinates.html#sphx-glr-examples-api-parallel-coordinates-py

Even looking through code, there's no obvious place where this is done.

• I imagine most plugins could statically define what inputs they need, why is it dynamic?
• If that's not possible, there should be some documented way to figure this out.