refactor: move structured output support outside LLM Node (#21565)

Co-authored-by: Novice <novice12185727@gmail.com>

api/core/llm_generator/prompts.py

@@ -291,3 +291,21 @@ Your task is to convert simple user descriptions into properly formatted JSON Sc
 
 Now, generate a JSON Schema based on my description
 """  # noqa: E501
+
+STRUCTURED_OUTPUT_PROMPT = """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:
+    {"additionalProperties": false, "properties": {"age": {"type": "number"}, "name": {"type": "string"}}, "required": ["name", "age"], "type": "object"}
+
+    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}}
+"""  # noqa: E501