[SPARK-3726] [MLlib] Allow sampling_rate not equal to 1.0 in RandomForests

I've added support for sampling_rate not equal to 1.0 . I have two major questions.

1. A Scala style test is failing, since the number of parameters now exceed 10.
2. I would like suggestions to understand how to test this.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #4073 from MechCoder/spark-3726 and squashes the following commits:

8012fb2 [MechCoder] Add test in Strategy
e0e0d9c [MechCoder] TST: Add better test
d1df1b2 [MechCoder] Add test to verify subsampling behavior
a7bfc70 [MechCoder] [SPARK-3726] Allow sampling_rate not equal to 1.0