SharedChannelOutboundMessage is always json encoded

[daviddawson]

SharedSocketRoute.java:65
Codecs.EncodingResult result = codecs.encode(outboundMessage, new String[] {"application/json"});

This is done this way because the discovery isn't available to sniff the acceptable content types of the remote, and we don't have this type of state naturally bound to the entire channel when it is composed.

This forces a json encoding at the low level when it may not be necessary.