Support creating msgpack request bodies

Hello, I have a number of projects using MessagePack encoding as opposed to JSON. [MessagePack]( is practically a binary representation of JSON, so in a way it sits in the middle between the flexible/verbose/human-readable JSON and the strict/binary protocol buffers. It would be great for my use cases to have support for creating MessagePack payloads to be send via POST/PUT (at least that's my main use case). I could envision this happening in basically 2 ways: • have a msgpack option in addition to JSON for the body content. The user would provide JSON content which Isomnia would encode appropriately before sending • have a msgpack option which would allow the user to select a binary file whose contents would be used as request body contents. Both options would result in the content-type header set to application/x-msgpack For interpreting responses, it could behave in a similar way: • when content-type: application/x-msgpack is received, th…