Roughly implement "harbormaster.artifact.search"

Summary: Ref T13438. This is a sort of minimal plausible implementation.

Test Plan: Used "harbormaster.artifact.search" to query information about artifacts.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13438

Differential Revision: https://secure.phabricator.com/D20878