use matrix to docker build in parallel

[nigelwtf]

Feel free to reject as this is a bit out of scope, but I saw an easy opportunity to reduce build time by more than half. I'm hoping this change will bring the exec time down to 5-6 minutes.

The crux of the build time is building the docker images and what I've implemented puts the build args into a matrix in the build-docker step so each entry runs simultaneously (or at least as fast as we get assigned workers from GH actions).

Changes

• Split the "build" step into setup, release-jars-and-artifacts, build-docker, build-docker-ce, finalize to cover each phase of the release
• Use upload artifacts to persist JARs (and dep checker reports) between steps