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

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

vllm/v1/engine/llm_engine.py

@@ -230,6 +230,9 @@ class LLMEngine:
 
         return processed_outputs.request_outputs
 
+    def get_vllm_config(self):
+        return self.vllm_config
+
     def get_model_config(self):
         return self.model_config