Update compose env var

docker-compose.build.yml

@@ -7,6 +7,8 @@ services:
     build:
       context: frontend
       dockerfile: Dockerfile
+    environment:
+      PUBLIC_BACKEND_URL: ${PUBLIC_BACKEND_URL}
 
   version_tag:
     extends: frontend

docker-compose.prod.yml

@@ -8,5 +8,6 @@ services:
       ORIGIN: "${ORIGIN}"
       PORT: 8000
       BODY_SIZE_LIMIT: 0
+      PUBLIC_BACKEND_URL: ${PUBLIC_BACKEND_URL}
     ports:
       - 127.0.0.1:8000:8000