[OBJECT-5378] support prepare locally flag

Signed-off-by: m.malygina <m.malygina@yadro.com>

src/frostfs_testlib/load/load_config.py

@@ -178,6 +178,10 @@ class LoadParams:
     min_iteration_duration: Optional[str] = metadata_field(
         all_load_scenarios, None, "K6_MIN_ITERATION_DURATION", False
     )
+    # Prepare/cut objects locally on client before sending
+    prepare_locally: Optional[bool] = metadata_field(
+        [LoadScenario.gRPC, LoadScenario.gRPC_CAR], None, "PREPARE_LOCALLY", False
+    )
     # Specifies K6 setupTimeout time. Currently hardcoded in xk6 as 5 seconds for all scenarios
     # https://k6.io/docs/using-k6/k6-options/reference/#setup-timeout
     setup_timeout: Optional[str] = metadata_field(all_scenarios, None, "K6_SETUP_TIMEOUT", False)