separate docker hub username and namespace (#11)

Author: dennisvang

.github/workflows/docker-publish.yml

@@ -36,7 +36,7 @@ jobs:
         with:
           # e.g. fairdata/fairdatapoint
           images: |
-            ${{ vars.DOCKER_HUB_USERNAME }}/${{ vars.DOCKER_IMAGE_NAME }}
+            ${{ vars.DOCKER_HUB_NAMESPACE }}/${{ vars.DOCKER_IMAGE_NAME }}
           # `latest` tag is generated by default
           tags: |
             type=ref,event=branch