R1:2160c4561990

Implement an "Attachments" behavior for Conduit Search APIs

Summary:
Ref T9964. We have various kinds of secondary data on objects (like subscribers, projects, paste content, Owners paths, file attachments, etc) which is somewhat slow, or somewhat large, or both.

Some approaches to handling this in the API include:

- Always return all of it (very easy, but slow).
- Require users to make separate API calls to get each piece of data (very simple, but inefficient and really cumbersome to use).