Pass commit authorship information to Buildkite
Fixes T12251. Ref T13189. See PHI610. The difficulty here is that we don't want to disclose Phabricator account information to Buildkite. We're comfortable disclosing information from git, etc.
- For commits, use the Identity to provide authorship information from Git.
- For revisions, use the local commit information on the Diff to provide the Git/Mercurial/etc author of the HEAD commit.
- Built commits and revisions in Buildkite via Harbormaster.
- I can't actually figure out how to see author information on the Buildkite side, but the values look sane when dumped locally.
Differential Revision: https://secure.phabricator.com/D19614