Separate github workflows for testing and deployment

[dennisvang]

The current build workflow takes care of both testing and deployment to docker hub:

https://github.com/FAIRDataTeam/FAIRDataPoint/blob/d0ca93f0ab993450a53f47bd3fd57270180c24f6/.github/workflows/build.yml

Instead of fully automated deployment to docker hub, it would be more convenient to have a separate, semi-automated deployment workflow that is triggered by a github release.

In addition, some cleanup is in order for the workflow.