fix file type not support when preview (#1841)

Co-authored-by: jyong <jyong@dify.ai>

api/services/file_service.py

@@ -133,7 +133,15 @@ class FileService:
 
         # extract text from file
         extension = upload_file.extension
-        if extension.lower() not in ALLOWED_EXTENSIONS:
+        etl_type = current_app.config['ETL_TYPE']
+        if etl_type == 'Unstructured':
+            allowed_extensions = ['txt', 'markdown', 'md', 'pdf', 'html', 'htm', 'xlsx',
+                                  'docx', 'csv', 'eml', 'msg', 'pptx', 'ppt', 'xml',
+                                  'jpg', 'jpeg', 'png', 'webp', 'gif', 'svg']
+        else:
+            allowed_extensions = ['txt', 'markdown', 'md', 'pdf', 'html', 'htm', 'xlsx', 'docx', 'csv',
+                                  'jpg', 'jpeg', 'png', 'webp', 'gif', 'svg']
+        if extension.lower() not in allowed_extensions:
             raise UnsupportedFileTypeError()
 
         text = FileExtractor.load(upload_file, return_text=True)