Expose internal insert function to pilot + optional ID during job insert

[brandur]

Here, expose encapsulated core insert logic to the pilot so extensions
can get access to it. We also add an optional ID to job insertion, a
property that's not used most of the time but useful for fine-tine
control over insertion that's required in some circumstances.

[brandur]

Dang it, somehow got two changes mixed up with each other. Lemme untangle this.

[brandur]

Actually, NM, the changes are correct. I ended up changing the signature of the insertion functions so they're a bit simpler (in more insertSharedResult) and use only exported types.