Refactor auto-deploy tagging

This is foundational work for gitlab-com/gl-infra/delivery#695 (closed), because we need a way to treat tag formatting (and possibly behavior, and deploying) differently depending on the packager being auto-deployed (Omnibus, CNG).

592dca3e - Move auto-deploy tagging to a packager-specific class

As Omnibus will use a different format than CNG, which may give way to even more formats, we needed to isolate the logic and formatting to their own classes.

b2bbe674 - Move Omnibus deployment into Omnibus tagger

If we successfully created a tag, we always wanted to create the same tag on the Deployer project.

Again, this logic could be different based on the packager, and CNG may want to deploy differently, so this logic has been isolated per-packager.

This greatly reduces the complexity of the PassingBuild class.