Split packaging job

[aangelisc]

The packaging step should be split so that each artifact that's packaged can be packaged and verified in isolation. This will allow us to upload artifacts that have passed verification and skip those that fail. This will then allow us to speed up successive rebuilds by skipping repackaging and reverifying artifacts that have previously succeeded.

[summerwollin]

@kminehart mentioned that if we move this to GitHub Actions it allows us to restart from the failed jobs.