add support for PerfXCloud (#1883)

### What problem does this PR solve?

#1853  add support for PerfXCloud

### Type of change


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

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

rag/llm/embedding_model.py

@@ -553,3 +553,10 @@ class CoHereEmbed(Base):
         return np.array([d for d in res.embeddings.float]), int(
             res.meta.billed_units.input_tokens
         )
+
+
+class PerfXCloudEmbed(OpenAIEmbed):
+    def __init__(self, key, model_name, base_url="https://cloud.perfxlab.cn/v1"):
+        if not base_url:
+            base_url = "https://cloud.perfxlab.cn/v1"
+        super().__init__(key, model_name, base_url)