Provide Conduit API for querying whether a release state version is still in use

Summary: This provides a Conduit API to determine whether a given release state version is still in use by any release.

Test Plan: Tested locally.

Reviewers: waynea, #koi

Reviewed By: waynea, #koi

JIRA Issues: KOI-1171

Differential Revision: https://code.pageuppeople.com/D3854

Risk Rating: 1