Add isClusterDevice to Almanac query

Summary: Ref T13076. This will be used by the metric collection system to iterate over the cluster devices.

Test Plan: Created some cluster and non-cluster devices, searched and saw expected results.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T13076

Differential Revision: https://secure.phabricator.com/D19368