fix model warning and use openwebui for preference based router demo

demos/use_cases/preference_based_routing/docker-compose.yaml

@@ -1,17 +1,14 @@
 services:
 
-  chatbot_ui:
-    build:
-      context: ../../shared/chatbot_ui
-      dockerfile: Dockerfile
+  open-web-ui:
+    image: ghcr.io/open-webui/open-webui:main
+    restart: always
     ports:
-      - "18080:8080"
+      - "8080:8080"
     environment:
-      - CHAT_COMPLETION_ENDPOINT=http://host.docker.internal:12000/v1
-    extra_hosts:
-      - "host.docker.internal:host-gateway"
-    volumes:
-      - ./arch_config.yaml:/app/arch_config.yaml
+      - DEFAULT_MODEL=gpt-4o-mini
+      - ENABLE_OPENAI_API=true
+      - OPENAI_API_BASE_URL=http://host.docker.internal:12000/v1
 
   jaeger:
     build: