batched-bench : add --output-format jsonl option (#9293)

`--output-format` is modeled after `llama-bench`'s options

common/common.h

@@ -275,6 +275,9 @@ struct gpt_params {
     bool spm_infill = false; // suffix/prefix/middle pattern for infill
 
     std::string lora_outfile = "ggml-lora-merged-f16.gguf";
+
+    // batched-bench params
+    bool batched_bench_output_jsonl = false;
 };
 
 void gpt_params_parse_from_env(gpt_params & params);