Allow keeping the result of an artifact build without cleaning it up

[becw]

Currently, the end of the artifact target prompts the user asking to push the artifact. If you say no, it will automatically clean up all changes to the artifact repo.

You can go in and look at the changes while the prompt sits there, if you like -- but that's not intuitive.

Instead, it should allow you to push, not push but keep the artifact, or discard the changes to the artifact -- so that there's an easy way for devs to look at the output of the build.

[becw]

This work is included in the 2.0.0-alpha3 release.