[Misc] Modularize CLI Argument Parsing in Benchmark Scripts (#19593)

Signed-off-by: reidliu41 <reid201711@gmail.com>
Co-authored-by: reidliu41 <reid201711@gmail.com>

benchmarks/benchmark_serving.py

@@ -875,7 +875,7 @@ def main(args: argparse.Namespace):
         save_to_pytorch_benchmark_format(args, result_json, file_name)
 
 
-if __name__ == "__main__":
+def create_argument_parser():
     parser = FlexibleArgumentParser(
         description="Benchmark the online serving throughput."
     )
@@ -1225,6 +1225,10 @@ if __name__ == "__main__":
         "script chooses a LoRA module at random.",
     )
 
-    args = parser.parse_args()
+    return parser
 
+
+if __name__ == "__main__":
+    parser = create_argument_parser()
+    args = parser.parse_args()
     main(args)