Add docker build and push github action

[eric-eclecticiq]

Motivation

Provide up-to-date images in the docker repository: https://hub.docker.com/r/eclecticiq/opentaxii

Changes

1. Add a job to do the docker actions in publish.yml
2. Pypi publish job is (still) only run on tag push
3. Docker job is not login and pushing in PR mode, only the build is tested.
4. Docker job pushes new images for master merge and pushed tags. A custom meta is provided as we use semver without the prefix v
5. The compose files accept a custom tag as an env var

Docker metadata documentation: https://github.com/docker/metadata-action

Note: I initially tested that a login/push worked with this MR in the following job.

[saaj]

CD (regarding artefacts) policy looks good.

Docker job is not login and pushing in PR mode, only the build is tested.

Note: I initially tested that a login/push worked with this MR in the following job.

But the job output looks like it did push. I assume it was with some rules temporarily omitted, and you removing the test image manually.