Update .zenodo.json and add a github citation file

[joergbrech]

We need to update the authors in the .zenodo.yml file!

It would be cool to have a citation file here as well. While we are at it, we should update our release CI/CD, such that the citation file is updated to point to the latest release. The workflow would be: Kepp zenodo file up-to-date, and in CI automatically create a PR with an updated citation.cff file after every new tag/release.