llama_cpp server: add missing top_k param to CreateChatCompletionRequest

`llama.create_chat_completion` definitely has a `top_k` argument, but its missing from `CreateChatCompletionRequest`. decision: add it

llama_cpp/server/app.py

@@ -169,6 +169,7 @@ class CreateChatCompletionRequest(BaseModel):
     model: str = model_field
 
     # llama.cpp specific parameters
+    top_k: int = 40,
     repeat_penalty: float = 1.1
 
     class Config: