Summary:
Depends on D19247. Ref T13109. When we receive an SSH request, generate a random unique ID for the request. Then thread it down through the process tree.
The immediate goal is to let the `ssh-exec` process coordinate with `commit-hook` process and log information about read and write lock wait times. Today, there's no way for `ssh-exec` to interact with the `PushEvent`, but this is the most helpful place to store this data for users.
Test Plan: Made pushes, saw the `PushEvent` table populate with a random request ID. Exported data and saw the ID preserved in the export.
Maniphest Tasks: T13109
Differential Revision: https://secure.phabricator.com/D19249
