add CI job to clear space

Author: etwk

.github/workflows/docker-image.yml

@@ -8,6 +8,14 @@ jobs:
   build-and-push:
     runs-on: ubuntu-latest
     steps:
+
+    - name: Free Disk Space (Ubuntu)
+      uses: jlumbroso/free-disk-space@main
+      with:
+        # this might remove tools that are actually needed,
+        # when set to "true" but frees about 6 GB
+        tool-cache: true
+
     - name: Check Out Repo
       uses: actions/checkout@v3