Add "/server_info" endpoint in api_server to retrieve the vllm_config. (#16572)

Signed-off-by: Xihui Cang <xihuicang@gmail.com>

vllm/engine/async_llm_engine.py

@@ -1167,6 +1167,10 @@ class AsyncLLMEngine(EngineClient):
                                             exception=asyncio.CancelledError,
                                             verbose=self.log_requests)
 
+    async def get_vllm_config(self) -> VllmConfig:
+        """Get the vllm configuration of the vLLM engine."""
+        return self.engine.get_vllm_config()
+
     async def get_model_config(self) -> ModelConfig:
         """Get the model configuration of the vLLM engine."""
         return self.engine.get_model_config()