[SPARK-11875][ML][PYSPARK] Update doc for PySpark HasCheckpointInterval

* Update doc for PySpark ```HasCheckpointInterval``` that users can understand how to disable checkpoint.
* Update doc for PySpark ```cacheNodeIds``` of ```DecisionTreeParams``` to notify the relationship between ```cacheNodeIds``` and ```checkpointInterval```.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #9856 from yanboliang/spark-11875.