Adding cdn support with compose

Now when you upload a file, the path is stored to the db and the file is
accesible on the client with : `localhost:8000/cdn/3ed026aa-366f-4f33-bc51-fb59d37e35ee.png` for instance.

compose.yaml

@@ -12,11 +12,18 @@ services:
     build: backend/.
     ports:
       - "8080:8080"
+    volumes:
+      - cdn:/backend/cdn
     ulimits:
       nofile:
         soft: 65536
         hard: 65536
   front:
     build: frontend/.
+    volumes:
+      - cdn:/app/front/dist/cdn
     ports:
       - "8000:8080"
+
+volumes:
+  cdn: