Add dynamic variable support to Assistant model and related components

- Introduce dynamic variable definitions in AssistantConfig and Assistant models, allowing for flexible prompt customization.
- Implement validation for dynamic variable names and types in the schema.
- Update backend services and routes to handle dynamic variables in assistant configurations and runtime processing.
- Enhance frontend components to support dynamic variable definitions, including a new editor for managing variables.
- Add tests to ensure proper functionality and validation of dynamic variables in various scenarios.

backend/services/conversation_history.py

@@ -40,8 +40,9 @@ class ConversationRecorder:
         assistant_name: str,
         channel: str,
         runtime_mode: str,
+        session_id: str | None = None,
     ) -> "ConversationRecorder | None":
-        session_id = f"conv_{uuid4().hex[:20]}"
+        session_id = session_id or f"conv_{uuid4().hex[:20]}"
         try:
             async with SessionLocal() as db:
                 db.add(