chore: adopt StrEnum and auto() for some string-typed enums (#25129)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

api/core/prompt/simple_prompt_transform.py

@@ -1,7 +1,7 @@
-import enum
 import json
 import os
 from collections.abc import Mapping, Sequence
+from enum import StrEnum, auto
 from typing import TYPE_CHECKING, Any, Optional, cast
 
 from core.app.app_config.entities import PromptTemplateEntity
@@ -25,9 +25,9 @@ if TYPE_CHECKING:
     from core.file.models import File
 
 
-class ModelMode(enum.StrEnum):
-    COMPLETION = "completion"
-    CHAT = "chat"
+class ModelMode(StrEnum):
+    COMPLETION = auto()
+    CHAT = auto()
 
 
 prompt_file_contents: dict[str, Any] = {}