Handle how to encode data for different output sinks

[supernomad]

So right now only protond is only capable of outputing the entire event structure as json encoded data. This is fine for testing and certain output sinks, however not all of them can support this data structure. The idea would be to allow for designating the final data and structure to send to the different outputs, and potentially allowing different outputs have different data encoding.

This could mean just having different output plugins for each of the different supported output sinks, but that means that any new sink will require direct development of protond. The idea would be to allow defining this structure during the filter process.