Update LLM configuration to support FastGPT integration. Modify requirements to include fastgpt-python-sdk, enhance greeting messages, and adjust LLM service creation to handle app_id. Implement welcome text fetching for FastGPT and improve context handling in the pipeline based on LLM provider. Update related configurations and properties for better integration.

engine/main.py

@@ -59,6 +59,9 @@ def create_app(config_path: str = "config.json") -> FastAPI:
                 "product_image_input": True,
             },
             "demo": webpage_mount,
+            "llm_backend": (
+                "fastgpt" if config.services.llm.is_fastgpt else "openai"
+            ),
             "llm_provider": config.services.llm.provider,
             "stt_provider": config.services.stt.provider,
             "tts_provider": config.services.tts.provider,