chore(ci): 0.12.0 s3 release fixes (#6689)

* chore(ci): 0.12.0 s3 release fixes

Fixes a couple of issues discovered with the 0.12.0 release:

* Removing old artifacts wasn't using --recursive so it didn't match
  anything
* I updated the redirection of artifacts to use `aws s3api` to list the
  objects rather than local file names to make it easier to run locally
  without having the built artifacts
* Refactored the latest channel artifact upload to just do one iteration
  over all of the different folders that are uploaded to

Signed-off-by: Jesse Szwedko <jesse@szwedko.me>