Consider providing different URIs for the different stages in the coprocessor request lifecycle

[grzn]

Today, the coprocessor needs to read the entire (and parse) the entire request body in order to figure out what request stage is.

This parsing can be heavy in some languages, and it would be nice performance improvement to be able to configure different URIs for the different request stages, so in the co-processor we wold be able to internally route the request to the relevant code without needed in to read the entire request body.