CNG: Refactor containers to fetch and build pattern

Summary

The gitlab-container-registry needs to be refactored to use our current pattern of downloading/extracting code in a separate shell script and not in the container definition.

In reality, we need to make a larger concerted effort to improve the maintainability of these image, which includes DRY-ing patterns which are common across all containers.

Current behavior

Several containers perform Fetch & Build are in a single RUN, and a complex one with many ... \ && ... \ && ....

Expected behavior

Use gitlab-fetch for UBI where appropriate
Use scripts/download (& scripts/build) where appropriate for external sources.
- scripts/download implements functionality to ensure checksums
Use consistent, DRY fetching method for Debian
- Ideally, independent of git calls