R1:5b22412f246e

Support data export on push logs

Summary: Depends on D18967. Ref T13049. Nothing too fancy going on here.

Test Plan: Exported push logs, looked at the export, seemed sensible.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13049

Differential Revision: https://secure.phabricator.com/D18968