[core-kit] Improve code/runJavascript schema

[aomarks]

1. Add a port to runJavascript for configuring the input schema (there is already one called schema but it only sets the output schema -- we want input and output -- so I think we rename schema to outputSchema and add a new inputSchema port).

2. Return the configured schema from the describe function (again, we do this for output already, but not yet input).

3. Update the code utility function to pass those schemas (which we already collect as parameters to code) into the inputSchema and outputSchema port configurations of the runJavascript node it creates.