GEOMESA-446 Wire up TDI via WPS

The only issue I know of is that the TDI process must be ran with xml as the output type currently. json does not work. Currently, we embed the json timeseries inside of the xml output (unless there is a query hint specifying to return an encoded time series object rather than the timeseries in json form).
can you use the ```df``` object instead of replicating the dtf string here?