[Bugfix] Make deprecated `--task embedding` consistent with `--runner… (#29312)

Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>

vllm/config/model.py

@@ -584,6 +584,16 @@ class ModelConfig:
                     )
                 else:  # task == "auto"
                     pass
+            else:
+                # Neither generative nor pooling model - try to convert if possible
+                if is_pooling_task:
+                    runner = "pooling"
+                    convert = _task_to_convert(self.task)
+                    msg_hint = (
+                        "Please replace this option with `--runner pooling "
+                        f"--convert {convert}` to continue using this model "
+                        "as a pooling model."
+                    )
                 else:
                     debug_info = {
                         "architectures": architectures,