Support Xinference (#320)

### What problem does this PR solve?

Issue link:#299

### Type of change

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

rag/llm/cv_model.py

@@ -161,6 +161,22 @@ class OllamaCV(Base):
         except Exception as e:
             return "**ERROR**: " + str(e), 0
 
+class XinferenceCV(Base):
+    def __init__(self, key, model_name="", lang="Chinese", base_url=""):
+        self.client = OpenAI(api_key=key, base_url=base_url)
+        self.model_name = model_name
+        self.lang = lang
+
+    def describe(self, image, max_tokens=300):
+        b64 = self.image2base64(image)
+
+        res = self.client.chat.completions.create(
+            model=self.model_name,
+            messages=self.prompt(b64),
+            max_tokens=max_tokens,
+        )
+        return res.choices[0].message.content.strip(), res.usage.total_tokens
+
 
 class LocalCV(Base):
     def __init__(self, key, model_name="glm-4v", lang="Chinese", **kwargs):