gitlab-ci: add jobs to make and upload source packages
Also re-organize the packaging pipeline to do the main binary building in the "build" stage.
GitLab update will be applied on June 28th, between 8am and 10:30am, EDT (UTC-04:00). This site may have intermittent delays during that time.
Also re-organize the packaging pipeline to do the main binary building in the "build" stage.