feat: Add open benchmark template codegen (#1579)

## What does this PR do?

As title, add codegen for open-benchmark template

## test 

checked the new generated run.yaml file and it's identical before and
after the change

Also add small improvement to together template so that missing
TOGETHER_API_KEY won't crash the server which is the consistent user
experience as other remote providers

llama_stack/providers/remote/inference/together/config.py

@@ -26,5 +26,5 @@ class TogetherImplConfig(BaseModel):
     def sample_run_config(cls, **kwargs) -> Dict[str, Any]:
         return {
             "url": "https://api.together.xyz/v1",
-            "api_key": "${env.TOGETHER_API_KEY}",
+            "api_key": "${env.TOGETHER_API_KEY:}",
         }