Modify Enricher and readme to work with the js-sdk instead of GDK
This changes the instructions in the devkit for Snowplow and the Enricher configuration to work with the Events coming from the SDK instead of doing a workaround to work with the GDK.
This is more future-proof and in line, with how the stack should be used going forward, since we want to always use the our SDK(s) to send events.