Investigate "post-merge" jobs to promote packages

We currently built, test and publish packages in the same job. The idea is that if packages don't pass tests, we don't want to publish them at all, so we should abort the job before doing so. I was told at ONS that there may be a way to do this using "post-merge" jobs. I don't really have a good handle on what this is or how it could work, but I should look into it.