use registry for images-serve

.gitmodules

-[submodule "image-service"]
-	path = image-service
-	url = https://git.chaotikum.org/chaotikum/infra/icebox-image-service.git

docker-compose.yml

@@ -15,7 +15,7 @@ services:
     depends_on:
     - backend
   image-service:
-    build: image-service
+    image: registry.chaotikum.net/icebox/icebox-image-service
     restart: always
     depends_on:
     - backend

image-service @ 588ddb98

-Subproject commit 588ddb98a137d61d41c71c9d2833e20937a3b95e