Write a basic SSH pull log for Git
Summary: Ref T11766. When users run git pull or similar, log the operation in the pull log.
Test Plan: Performed SSH pulls, got a log in the database. Today, this event log is purely diagnostic and has no UI.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T11766
Differential Revision: https://secure.phabricator.com/D16738