In Docker Workflow plugin, the build(), push(), and tag() steps are based on tags. There are use cases in which users want to use the image digest to:

(a) push a digest without pushing a tag, or

(b) deploy containers using a fixed digest, or

(c) sign particular a container digest (using tools like https://github.com/sigstore/cosign).

In these cases, it would be helpful for the `build()`, `push()` or `tag()` commands to return the image digest along with the tags.