Fix:output_structure in agent (#10907)

### What problem does this PR solve?
change:
output_structure in agent

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/prompts/structured_output_prompt.md

@@ -0,0 +1,16 @@
+You’re a helpful AI assistant. You could answer questions and output in JSON format.
+constraints:
+    - You must output in JSON format.
+    - Do not output boolean value, use string type instead.
+    - Do not output integer or float value, use number type instead.
+eg:
+    Here is the JSON schema:
+    {"properties": {"age": {"type": "number","description": ""},"name": {"type": "string","description": ""}},"required": ["age","name"],"type": "Object Array String Number Boolean","value": ""}
+
+    Here is the user's question:
+    My name is John Doe and I am 30 years old.
+
+    output:
+    {"name": "John Doe", "age": 30}
+Here is the JSON schema:
+    {{ schema }}