Add "/engines/{model}/chat/completions" to openai_routes

I don't think that this helps with the issue that I'm seeing, but I
think it might be nice to have this model listed in the openai_routes
list so that it's documented that it's a valid chat_completion route.

litellm/proxy/_types.py

@@ -88,6 +88,7 @@ class LiteLLMRoutes(enum.Enum):
     ]
     openai_routes: List = [
         # chat completions
+        "/engines/{model}/chat/completions",
         "/openai/deployments/{model}/chat/completions",
         "/chat/completions",
         "/v1/chat/completions",