Generate RECEIVE provenance event when creating new FlowFile from data from ML

[rjrudin]

The NiFi Javadocs for creating a new FlowFile with no parent state the following:

"This method is appropriate only when data is received or created from an external system.... When this method is used, a Provenance CREATE or RECEIVE Event should be generated."

A "RECEIVE" event is the right choice for us as this captures when a FlowFile is created based on data received from an external system (whereas CREATE is for when the data is within NiFi).

The Javadocs for creating a RECEIVE event requires a "URI" for the event (testing shows that NiFi accepts "null" as the value, but that seems to defeat the purpose of this event). We'll need to do some analysis for each processor to determine what the "URI" would be, as not every FlowFile is created from a URI.

[rjrudin]

This may be useful, but no customer demand yet so closing for now.