add dockerfile for nginx

docker-compose.yaml

@@ -13,8 +13,9 @@ services:
       - "traefik.http.services.django-service.loadbalancer.server.port=8000"
 
   nginx:
-    context: .
+    build:
-    dockerfile: Dockerfile.nginx
+      context: .
+      dockerfile: Dockerfile.nginx
     volumes:
       - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
       - media_volume:/app/media:ro # ان‌جینکس فقط باید بخواند (امن‌تر)