[fs2<->camel] Support inbound in-out message exchanges for FS2

[krasserm]

[Daenyth]

@krasserm Do you have context around this? I might close it since it feels somewhat non-actionable. Which submodule wants this, and what feature in the converted api does it interact with?

[krasserm]

This is something already supported for the Akka-Camel integration but not yet implemented for FS2-Camel. When consuming a message from a Camel endpoint, you usually want to reply with an application-level response or an ACK after the message has been processed on FS2 side. At the moment, the FS2-Camel integration confirms consumption of a message immediately i.e. before the message is processed on FS2 side. For example, this may prevent a message re-delivery if a message was consumed from a Camel message queue but message processing fails on FS2 side. Following the implementation pattern in the link above, it should be rather straightforward to implement it for FS2-Camel as well.