makeDistinctValuesMap
This method creates a hashmap containing the distinct values of the table's columns
the input is a Table, the output is a hashmap with the following structure:
{
column1: {first_value_of_column1: occurence_count, second_value_of_column1: occurence_count,..},
column2: {first_value_of_column2: occurence_count, second_value_of_column2: occurence_count,..},
:
}