Enable @use_case and @multi_processor_use_case decorators to be added to Python Processors

Currently, Python processors have no way of articulating specific use cases and multi-processor use cases in their docs. Introduce new decorators to allow for these.

We use decorators here in order to keep the structure similar to that of Java but also because it offers a clean mechanism for defining the MultiProcessorUseCase, which becomes awkward if trying to include in the ProcessorDetails inner class.