Add Dify integration and enhance workflow node specifications

- Introduce new fields `dify_api_url` and `dify_api_key` in `AssistantConfig` for Dify API integration.
- Update `requirements.txt` to include `dify-client-python` for Dify SDK support.
- Modify `config_resolver` to handle Dify connection information.
- Add a new `globalNode` type in workflow specifications to provide unified settings across workflows.
- Enhance node specifications with additional constraints and default values for better configuration management.
- Update frontend components to support the new `globalNode` type and its properties, improving workflow editor functionality.

backend/models.py

@@ -79,6 +79,8 @@ class AssistantConfig(BaseModel):
     graph: dict = {}
 
     # 外部托管类型(fastgpt/dify/opencode)的连接信息:context/KB/tools 由对方服务端接管。
+    dify_api_url: str = ""
+    dify_api_key: str = ""
     fastgpt_api_url: str = ""
     fastgpt_api_key: str = ""
     fastgpt_app_id: str = ""