Rename `build_events` to `job_events`, take 2.
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11287 was reverted because it was causing migration errors.
Since https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11396 was merged, this can be re-applied.
This fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/31620