Expose `getDependentStoryFiles` API in JSON format

[ghengeveld]

From AP-4154

What

Add tracing method to CLI Node API.

Why

So that the VTA can run a trace command and show the results in a web UI.

How

Update the CLI so we have a Node API that allows us to use getDependentStoryFiles in a somewhat API-friendly manner (no logging, sensible object return value that's JSON serializable).