job chat: include rag results in final payload

[josephjclark]

When the assistant returns its chat output to Lightning, we should include some representation of what rag docs were included (section title, maybe page URL)

We can use this information for monitoring, evaluation, and also report it to the end user in the app

[josephjclark]

Maybe Elias can help us ensure that the returned rag metadat gets saved to the Lightning DB (so we can access it in Metabase)