Add workflow support and enhance runtime configuration in models and services

- Introduce RuntimeModelResource and RuntimeKnowledgeBase classes to manage workflow resources.
- Update AssistantConfig to include workflow_model_resources and workflow_knowledge_bases for better integration.
- Refactor validation and processing logic in routes and services to accommodate workflow types.
- Implement dynamic variable support for workflow assistants and enhance graph normalization.
- Add ToolExecutor for reusable tool execution across different assistant types.
- Update various services to ensure compatibility with new workflow features and improve error handling.

backend/schemas.py

@@ -138,7 +138,7 @@ class AssistantUpsert(CamelModel):
                 setattr(self, field, "")
         if "graph" not in allowed:
             self.graph = {}
-        if self.type != "prompt":
+        if self.type not in {"prompt", "workflow"}:
             self.tool_ids = []
             self.dynamic_variable_definitions = {}
         # 外部托管大脑只能 cascade,拦住不兼容的 realtime