This commit adds options to the Maven and Gradle plugins to publish
to a Docker registry the image generated by the image-building goal
and task.
The Docker registry auth configuration added in an earlier commit
was modified to accept separate auth configs for the builder/run
image and the generated image, since it is likely these images will
be stored in separate registries or repositories with distinct
auth required for each.
Fixes gh-21001
09b627d232