Support Xinference (#321)

### What problem does this PR solve?

Issue link:#299

### Type of change

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

docs/xinference.md

+# Xinference
+
+<div align="center" style="margin-top:20px;margin-bottom:20px;">
+<img src="https://github.com/infiniflow/ragflow/assets/12318111/2c5e86a7-807b-4d29-bd2b-f73fb1018866" width="130"/>
+</div>
+
+Xorbits Inference([Xinference](https://github.com/xorbitsai/inference)) empowers you to unleash the full potential of cutting-edge AI models. 
+
+## Install
+
+- [pip install "xinference[all]"](https://inference.readthedocs.io/en/latest/getting_started/installation.html)
+- [Docker](https://inference.readthedocs.io/en/latest/getting_started/using_docker_image.html)
+
+To start a local instance of Xinference, run the following command:
+```bash
+$ xinference-local --host 0.0.0.0 --port 9997
+```
+## Launch Xinference
+
+Decide which LLM you want to deploy ([here's a list for supported LLM](https://inference.readthedocs.io/en/latest/models/builtin/)), say, **mistral**.
+Execute the following command to launch the model, remember to replace ${quantization} with your chosen quantization method from the options listed above:
+```bash
+$ xinference launch -u mistral --model-name mistral-v0.1 --size-in-billions 7 --model-format pytorch --quantization ${quantization}
+```
+
+## Use Xinference in RAGFlow
+
+- Go to 'Settings > Model Providers > Models to be added > Xinference'.
+    
+<div align="center" style="margin-top:20px;margin-bottom:20px;">
+<img src="https://github.com/infiniflow/ragflow/assets/12318111/bcbf4d7a-ade6-44c7-ad5f-0a92c8a73789" width="1300"/>
+</div>
+
+> Base URL: Enter the base URL where the Ollama service is accessible, like, http://<your-ollama-endpoint-domain>:11434
+
+- Use Xinference Models.
+
+<div align="center" style="margin-top:20px;margin-bottom:20px;">
+<img src="https://github.com/infiniflow/ragflow/assets/12318111/b01fcb6f-47c9-4777-82e0-f1e947ed615a" width="530"/>
+</div>
+<div align="center" style="margin-top:20px;margin-bottom:20px;">
+<img src="https://github.com/infiniflow/ragflow/assets/12318111/1763dcd1-044f-438d-badd-9729f5b3a144" width="530"/>
+</div>
\ No newline at end of file

rag/llm/cv_model.py

@@ -161,9 +161,10 @@ 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.client = OpenAI(api_key="xxx", base_url=base_url)
         self.model_name = model_name
         self.lang = lang