Add mechanism to receive errors from http interaction initial responses

[beanjo55]

Currently when using a http url to receive interactions, there's no way to get an error back from the initial response, like you would with /callback after a gateway received interaction. This adds complexity to developing and tracking & fixing errors in http interaction systems, where your response fails and you don't know it did or why.

[ckohen]

Maybe an additional, informational (HTTP only), interaction type or even a separate endpoint