Ref T12251. Currently the Buildkite API calls don't include any authorship information, making Buildkite's permission and notification system unusable for any builds triggered from Phabricator.

This probably wasn't noticed during initial development, as Buildkite will associate the build with the owner of the API key, so it probably appeared fine. But as soon as another user triggers a build plan, the Buildkite authorship information is incorrect.

This updates the Buildkite API call to include an "author" field containing the name and primary email address of the author of diffs and commits, which will allow Buildkite to match it against their list of verified email addresses and correctly associate builds.

Create a diff and a commit that trigger "Build with Buildkite" build plan steps. Verify the build author in the Buildkite interface shows the user name and email from Phabricator, and not the user that created the Buildkite API token.