make excel parsing configurable (#2517)

### What problem does this PR solve?

#2516

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/app/naive.py

     elif re.search(r"\.xlsx?$", filename, re.IGNORECASE):
         callback(0.1, "Start to parse.")
         excel_parser = ExcelParser()
-        sections = [(l, "") for l in excel_parser.html(binary) if l]
+        if parser_config.get("html4excel"):
+            sections = [(l, "") for l in excel_parser.html(binary, 12) if l]
+        else:
+            sections = [(l, "") for l in excel_parser(binary) if l]
 
     elif re.search(r"\.(txt|py|js|java|c|cpp|h|php|go|ts|sh|cs|kt|sql)$", filename, re.IGNORECASE):
         callback(0.1, "Start to parse.")

rag/llm/chat_model.py

 
         yield num_tokens_from_string(ans)
 
+
 class GeminiChat(Base):
 
     def __init__(self, key, model_name,base_url=None):