[SPARK-20768][PYSPARK][ML] Expose numPartitions (expert) param of PySpark FPGrowth.
[SPARK-20768][PYSPARK][ML] Expose numPartitions (expert) param of PySpark FPGrowth.

## 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.

(cherry picked from commit 139da116f130ed21481d3e9bdee5df4b8d7760ac)
Signed-off-by: Yanbo Liang <452ae006f36be6c70342f33f64bb6f6eb552689c@gmail.com>

publicRoman/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,publicRoman/spark,jlopezmalla/spark,jlopezmalla/spark,jlopezmalla/spark,publicRoman/spark,publicRoman/spark,publicRoman/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,jlopezmalla/spark,jlopezmalla/spark,publicRoman/spark,apache-spark-on-k8s/spark,publicRoman/spark,apache-spark-on-k8s/spark