change the default ensemble method to AlgoEnsembleBestByFold in AutoR… (#5722)

Change the default ensemble method

Signed-off-by: Mingxin Zheng
<18563433+mingxin-zheng@users.noreply.github.com>

Fixes Item 2 in #5564 .

### Description

A few sentences describing the changes proposed in this pull request.

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [x] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.

Signed-off-by: Mingxin Zheng <18563433+mingxin-zheng@users.noreply.github.com>

Author: mingxin-zheng

monai/apps/auto3dseg/auto_runner.py

@@ -268,7 +268,7 @@ def __init__(
 
         # intermediate variables
         self.num_fold = 5
-        self.ensemble_method_name = "AlgoEnsembleBestN"
+        self.ensemble_method_name = "AlgoEnsembleBestByFold"
         self.set_training_params()
         self.set_prediction_params()
         self.set_analyze_params()
@@ -473,7 +473,7 @@ def set_image_save_transform(self, kwargs):
             output_dir=output_dir, output_postfix=output_postfix, output_dtype=output_dtype, resample=resample, **kwargs
         )
 
-    def set_ensemble_method(self, ensemble_method_name: str = "AlgoEnsembleBestN", **kwargs):
+    def set_ensemble_method(self, ensemble_method_name: str = "AlgoEnsembleBestByFold", **kwargs):
         """
         Set the bundle ensemble method