handle messagepack and raw json before falling back to bytes decoding

Currently [`consume`](https://github.com/ISISComputingGroup/saluki/blob/main/src/consume.rs) deserialises flatbuffer encoded messages when it receives them from a topic.

As a failover, it should be able to:

try `msgpack` (as the bluesky stuff serialises with it)
if this fails, just try and print the payload as bytes