ci: use harbor buildkit image for buildx

Jenkinsfile

@@ -140,7 +140,9 @@ spec:
               fi
               sleep 2
             done
-            docker buildx create --name bstein-builder --driver docker-container --bootstrap --use || docker buildx use bstein-builder
+            docker buildx create --name bstein-builder --driver docker-container \
+              --driver-opt image=registry.bstein.dev/bstein/buildkit:buildx-stable-1 \
+              --bootstrap --use || docker buildx use bstein-builder
           '''
         }
       }