WIP: Simplify process of making releases

[Sophietje]

This PR adds a Github workflow for (1) drafting a release, and (2) uploading Docker images to the registry.

This will modify the way that we're currently making releases. I envision the following workflow:

1. User makes commit to prepare for the version release, changing the versions where needed (same as current first step)
2. User triggers Github Action via Github's interface, you will be asked to provide the new version (X.Y.Z) as input
3. Draft release is made by workflow (1)
4. When ready, user inspects the draft release made by the workflow. The user can make changes if necessary and 'publishes' it definitively
5. Docker images are made and uploaded by workflow (2)
6. User makes commit for next SNAPSHOT version (the same as current 7th step)
7. Inform the world

[Sophietje]

TODO: Fix upload of JARs to release, it currently cannot find the right files