code: def get_label_cols():
      return ["label"]
  
file_path: BigDL/python/orca/tutorial/NCF/process_spark_dataframe.py
imports: import os
  from pyspark.ml.feature import StringIndexer, MinMaxScaler, VectorAssembler
  from pyspark.ml import Pipeline
  from pyspark.sql.types import StructField, StructType, IntegerType, LongType, ArrayType, StringType
  from pyspark.sql.functions import udf, lit, collect_list, explode, concat
  from bigdl.orca import OrcaContext
label_desc: Use image node_id 8 for calling a global function with example usage: get_label_cols() and returns: list