Use java client for docker access

"jib" does not work well with all docker registries, e.g. Portus does not show images pushed with "jib". "jibDockerBuild" requires a docker image containing a docker binary. That is not appropriate for modern CI processes which require "plain" docker images, e.g. a plain java image for executing gradle.

So it would be nice if "jibDockerBuild" would use a java based docker client instead of expecting docker to be installed. This way a lean "docker in docker" approach can be used to provide the docker unix socket to the "plain" build container. This approach avoids any incompatibilities like e.g. the Portus problem or extremely slow upload speeds (compared to docker push) into GitLab repositories.

E.g. fabric8s docker maven plugin already does it this way. Another way would be using https://github.com/amihaiemil/docker-java-api.