Add ping command to test ping API (#12757)

### What problem does this PR solve?

As title.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

api/apps/system_app.py

@@ -178,7 +178,7 @@ def healthz():
 
 
 @manager.route("/ping", methods=["GET"])  # noqa: F821
-def ping():
+async def ping():
     return "pong", 200