Feat: add gpustack model provider (#4469)

### What problem does this PR solve?

Add GPUStack as a new model provider.
[GPUStack](https://github.com/gpustack/gpustack) is an open-source GPU
cluster manager for running LLMs. Currently, locally deployed models in
GPUStack cannot integrate well with RAGFlow. GPUStack provides both
OpenAI compatible APIs (Models / Chat Completions / Embeddings /
Speech2Text / TTS) and other APIs like Rerank. We would like to use
GPUStack as a model provider in ragflow.

[GPUStack Docs](https://docs.gpustack.ai/latest/quickstart/)

Related issue: https://github.com/infiniflow/ragflow/issues/4064.

### Type of change

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



### Testing Instructions
1. Install GPUStack and deploy the `llama-3.2-1b-instruct` llm, `bge-m3`
text embedding model, `bge-reranker-v2-m3` rerank model,
`faster-whisper-medium` Speech-to-Text model, `cosyvoice-300m-sft` in
GPUStack.
2. Add provider in ragflow settings.
3. Testing in ragflow.

rag/llm/embedding_model.py

@@ -30,7 +30,7 @@ import asyncio
 from api import settings
 from api.utils.file_utils import get_home_cache_dir
 from rag.utils import num_tokens_from_string, truncate
-import google.generativeai as genai 
+import google.generativeai as genai
 import json
 
 
@@ -799,3 +799,14 @@ class VolcEngineEmbed(OpenAIEmbed):
         ark_api_key = json.loads(key).get('ark_api_key', '')
         model_name = json.loads(key).get('ep_id', '') + json.loads(key).get('endpoint_id', '')
         super().__init__(ark_api_key,model_name,base_url)
+
+class GPUStackEmbed(OpenAIEmbed):
+    def __init__(self, key, model_name, base_url):
+        if not base_url:
+            raise ValueError("url cannot be None")
+        if base_url.split("/")[-1] != "v1-openai":
+            base_url = os.path.join(base_url, "v1-openai")
+
+        print(key,base_url)
+        self.client = OpenAI(api_key=key, base_url=base_url)
+        self.model_name = model_name