feat(prompt-optimizer): add prompt optimization APIs and database tables

- Added API endpoints for prompt optimization:
  * POST /prompt/sessions: Create a new prompt optimization session
  * GET /prompt/sessions/{session_id}: Retrieve session message history
  * POST /prompt/sessions/{session_id}/messages: Send message and get optimized prompt
  * PUT /prompt/model: Create or update system prompt model configuration

- Added database models for prompt optimization:
  * prompt_opt_session: Stores session metadata
  * prompt_opt_session_history: Stores session message history
  * prompt_opt_message: Stores user and assistant messages
  * prompt_opt_model_config: Stores system prompt model configurations

- Updated service layer to handle message creation, prompt optimization, and variable parsing
- Added corresponding Pydantic schemas for request and response validation

api/app/models/models_model.py

@@ -15,6 +15,25 @@ class ModelType(StrEnum):
     EMBEDDING = "embedding"
     RERANK = "rerank"
 
+    @classmethod
+    def from_str(cls, value: str) -> "ModelType":
+        """
+        Get a ModelType enum instance from a string value.
+
+        Args:
+            value (str): The string representation of the model type.
+
+        Returns:
+            ModelType: The corresponding ModelType enum object.
+
+        Raises:
+            ValueError: If the given value does not match any ModelType.
+        """
+        try:
+            return cls(value)
+        except ValueError:
+            raise ValueError(f"Invalid ModelType: {value}")
+
 
 class ModelProvider(StrEnum):
     """模型提供商枚举"""