## What changes were proposed in this pull request?

Expose numPartitions (expert) param of PySpark FPGrowth.

## How was this patch tested?

+ [x] Pass all unit tests.

Author: Yan Facai (颜发才) <facai.yan@gmail.com>

Closes #18058 from facaiy/ENH/pyspark_fpg_add_num_partition.