R1:1258ed348b44

Add return type to `conduit.query`

Summary: Fixes T6950. Adds the return type of Conduit API methods to the `conduit.query` call.

Test Plan: Called `echo '{}' | arc call-conduit conduit.query` and verified that the return types were present in the response.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T6950

Differential Revision: https://secure.phabricator.com/D11466