Add _predict_model_on_cpu for RandomForestClassifier (rapidsai#5148)

Closes rapidsai#5008

Authors:
  - Micka (https://github.com/lowener)
  - Dante Gama Dessavre (https://github.com/dantegd)

Approvers:
  - Dante Gama Dessavre (https://github.com/dantegd)

URL: rapidsai#5148

python/cuml/dask/ensemble/randomforestclassifier.py

@@ -188,6 +188,10 @@ def _construct_rf(
             **kwargs
         )
 
+    @staticmethod
+    def _predict_model_on_cpu(model, X, convert_dtype):
+        return model._predict_model_on_cpu(X, convert_dtype=convert_dtype)
+
     def get_summary_text(self):
         """
         Obtain the text summary of the random forest model