refactor: use EnumText for dataset and replace string literals 4 (#33606)

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

api/core/callback_handler/index_tool_callback_handler.py

@@ -12,7 +12,7 @@ from core.rag.models.document import Document
 from extensions.ext_database import db
 from models.dataset import ChildChunk, DatasetQuery, DocumentSegment
 from models.dataset import Document as DatasetDocument
-from models.enums import CreatorUserRole
+from models.enums import CreatorUserRole, DatasetQuerySource
 
 _logger = logging.getLogger(__name__)
 
@@ -36,7 +36,7 @@ class DatasetIndexToolCallbackHandler:
         dataset_query = DatasetQuery(
             dataset_id=dataset_id,
             content=query,
-            source="app",
+            source=DatasetQuerySource.APP,
             source_app_id=self._app_id,
             created_by_role=(
                 CreatorUserRole.ACCOUNT