Automate tagging and publishing Docker image with release version

[juhoinkinen]

Now for all commits to master the Drone build pipeline is triggered and the Docker image is published in quay.io repo with tag latest. I uploaded manually the image with tag 1.3.2 (using git checkout tags/mauiserver-1.3.2. and docker build -t quay.io/natlibfi/mauiserver:1.3.2 and pushing).

When doing a release, it would be good to automate publishing the image with the release version tag. This could be done with auto_tag feature of Drone's Docker-plugin as in Annif's Drone pipeline. However, now releases have git tags with prefix mauiserver-, which auto_tag does not handle, I think.

However, if there won't be new releases often, the manual way will suffice.

Also, there could be a dedicated stage in Dockerfile (or a different Dockerfile) for the release build, which would download the artifact from maven central instead of building from source.