Fix docker image labels for merges to main and for releases

[tkilias]

Background

• we currently update the docker image with the label latest for each merge/push to main, but it would be better to have it point to the last release.

Acceptance Criteria

We need a CI task

• publish-main, which builds the image whenever main get updated (merge, push), it then builds the docker image for the main branch and pushes it with the label main.
• publish-release, which builds the image whenever we create a release (release tag gets created), it then builds the docker image for the commit of this release and pushes it with the release name as label to docker hub. Furthermore, it advances the latest tag to release tag and builds the image also with the label latest and pushes this as well to docker hub.

bash starter_scripts/build_docker_runner_image.sh <label>
bash starter_scripts/push_docker_runner_image.sh <label>