[Feature] Allow ConfigurationGenerator to register custom annotation handlers

[shochdoerfer]

Currently the ConfigurationGenerator is working with a fixed set of annotations which is ok for now but in the future I`d like to see a way to add custom annotation handlers which should be able to generate methods (and maybe more?) in the generated proxy class so that frameworks could add own annotations (e.g. an annotation to configure the routing or security settings).

[shochdoerfer]

Instead of generating magic methods that can be called from the bean configuration method we should simply extend the "Parameter" mechanism and allow to inject those "values". That way the generated code will be syntactically correct - which is one of the key features of Disco.