github-actions: refactor docker

[v1v]

What does this PR do?

Use https://docs.docker.com/build/building/multi-stage/ to generate the Docker image. This will help using Docker natively to fetch the artifacts with some build-args (whether using the standalone files or fetching from Sonatype given the release version). This will make the Docker image agnostic to the host.

In addition, it removes the complexity of using shell scripts. and use native GitHub action support with tag and label detection.

Generate docker images for the snapshots using the docker tag name test-latest.

Finally, this will help us provide some provenance for the docker images, which was not done as docker build/push was in shell scripts.

Checklist

• [ ] This is an enhancement of existing features, or a new feature in existing plugins
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] I have added tests that prove my fix is effective or that my feature works
  • [ ] Added an API method or config option? Document in which version this will be introduced
  • [ ] I have made corresponding changes to the documentation
• [ ] This is a bugfix
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] I have added tests that would fail without this fix
• [ ] This is a new plugin
  • [ ] I have updated CHANGELOG.asciidoc
  • [ ] My code follows the style guidelines of this project
  • [ ] I have made corresponding changes to the documentation
  • [ ] I have added tests that prove my fix is effective or that my feature works
  • [ ] New and existing unit tests pass locally with my changes
  • [ ] I have updated supported-technologies.asciidoc
  • [ ] Added an API method or config option? Document in which version this will be introduced
  • [ ] Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• [ ] This is something else
  • [ ] I have updated CHANGELOG.asciidoc

[SylvainJuge]

The https://github.com/elastic/apm-agent-java/pull/3652 PR is also likely to introduce a few other conflicts, but the underlying issue might be implicitly fixed by only downloading and not as a fallback of the local build.