[Request] allow to override DecodeException throwing logic in Feign

[tomaszszlek]

Hi, as mentioned in this issue #725, it is not possible to customise behaviour of throwing by wrapping by Feign all exceptions thrown from Custom Decoders into DecodeException. It would be nice to have control over it and be able to configure Feign to throw original exception instead of DecodeException. While I understand its considered fatal error I might want to convert this into my business, standard fatal exception. Currently its only possible outside Feign client. It would be handy to configure it in Feign.Builder.