add support for LM Studio (#1663)

### What problem does this PR solve?

#1602 

### Type of change

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

---------

Co-authored-by: Zhedong Cen <cenzhedong2@126.com>

rag/llm/chat_model.py

@@ -976,3 +976,15 @@ class NvidiaChat(Base):
             yield ans + "\n**ERROR**: " + str(e)
 
         yield total_tokens
+
+
+class LmStudioChat(Base):
+    def __init__(self, key, model_name, base_url):
+        from os.path import join
+
+        if not base_url:
+            raise ValueError("Local llm url cannot be None")
+        if base_url.split("/")[-1] != "v1":
+            self.base_url = join(base_url, "v1")
+        self.client = OpenAI(api_key="lm-studio", base_url=self.base_url)
+        self.model_name = model_name