Move checkout and login from Docker actions to workflow

[yannick-roeder]

Additionally the following changes were done:

• rename docker-publisher -> image-repository
• remove tagging in build action (only necessary when publishing)
• change default tag for docker images from ${{ github.run_id }} to pipeline-${{ github.run_id }}-git-${GITHUB_SHA::8}
• allow both docker-registry and image-repository to be optional in image name
• introduce input for retention-days of GitHub artifact (default: 1)