dot-calculate_columns_means: calculate list of columns mean of target by column value
In ddzr/XL.RPackage: XL R Package

Output a data.table that contains list of columns mean target by column value

.calculate_columns_means(
  mean_target_colnames,
  target_colname,
  data,
  min_samples_leaf = 0,
  smoothing = 1
)

`mean_target_colnames`	list of column names that needs mean target encoding
`target_colname`	target column name, should be numeric
`data`	dataset used to calculate mean target, usually is the training dataset
`min_samples_leaf`	minimum quantity per column value we consider needs to be calculate mean.
`smoothing`	used to adjust column value mean target from grand target value, default value 1 is to ignore grand target value