Apply base-image security updates to a buildpacks-built app image in seconds with pack rebase instead of a full rebuild.

Documented steps

1. Concept: 'Rebase allows app developers or operators to rapidly update an app image when its runtime base image has changed... By using image layer rebasing, this command avoids the need to fully rebuild the app' (https://buildpacks.io/docs/for-app-developers/concepts/rebase/).
2. Basic usage: `pack rebase my-app:my-tag` — swaps the app image's run-image (base) layers for the latest version of the run image it was built against.
3. Publish the rebased image directly to a registry with `pack rebase myapp:tag --publish` — 'The previous application image must also reside in the registry.' The docs note --publish 'is optimal when using a registry in comparison to the docker daemon' (https://buildpacks.io/docs/for-platform-operators/how-to/integrate-ci/pack/cli/pack_rebase/).
4. Optional flags: `--run-image <image>` to rebase onto a specific run image; `--previous-image <ref>` to rebase a specific tag/digest while writing the result to a different <image-name> (avoids overwriting the original); `--pull-policy always|never|if-not-present` (default always); `--force` to skip target validation (Platform API >= 0.12); `--insecure-registry` (API >= 0.13).