Conversion fail for ov::hint::performance_mode with UNDEFINED value (#15629)

* Update ov::hint::performance_hint UNDEFINED value from empty string to "UNDEFINED".

* Update benchmark Python version.

* Update.

* Update.

* Update.

* Update the description about hint setting within benchmark APP README and help message.

tools/benchmark_tool/openvino/tools/benchmark/main.py

@@ -112,7 +112,7 @@ def main():
                 if is_flag_set_in_command_line('hint'):
                     if args.perf_hint=='none':
                         logger.warning(f"No device {device} performance hint is set.")
-                        args.perf_hint = ''
+                        args.perf_hint = 'UNDEFINED'
                 else:
                     args.perf_hint = "THROUGHPUT" if benchmark.api_type == "async" else "LATENCY"
                     logger.warning(f"Performance hint was not explicitly specified in command line. " +