Feat: add LLM provider PPIO (#5013)

### What problem does this PR solve?

Add a LLM provider: PPIO

### Type of change

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

rag/llm/__init__.py

@@ -75,6 +75,7 @@ from .chat_model import (
     UpstageChat,
     NovitaAIChat,
     SILICONFLOWChat,
+    PPIOChat,
     YiChat,
     ReplicateChat,
     HunyuanChat,
@@ -220,6 +221,7 @@ ChatModel = {
     "Upstage": UpstageChat,
     "novita.ai": NovitaAIChat,
     "SILICONFLOW": SILICONFLOWChat,
+    "PPIO": PPIOChat,
     "01.AI": YiChat,
     "Replicate": ReplicateChat,
     "Tencent Hunyuan": HunyuanChat,