Current workflow runs tests and builds and deploys docker image both to private nexus (deprecated) and public docker hub.

• The private nexus repo is no longer operational, so we need to remove the nexus publication step.
• In addition, it is more convenient to have separate workflows for testing and for publication to docker hub.
• Also see if we can share the docker publication workflows with https://github.com/FAIRDataTeam/FAIRDataPoint and collect them in one place, viz. https://github.com/FAIRDataTeam/github-workflows