Streamline configuration for the same test applied to multiple columns

[phpisciuneri]

Currently, if I wanted to check for null values in each of the columns (age, occupation) of a table, the checks: section of the configuration file would contain something this:

- type: nullCheck
  column: age

- type: nullCheck
  column: occupation

Ideally, we should support a more streamlined config. Something like:

- type: nullCheck
  columns: age, occupation

We would need to decide how to handle optional parameters in the streamlined case. One option is that we do not support streamlining if any optional parameters are specified:

- type: nullCheck
  column: age
  threshold: 1%

- type: nullCheck
  column: occupation
  threshold: 5%

Another option would be to allow additional parameters to be streamlined and applied in the same order as the specified columns:

- type: nullCheck
  columns: age, occupation
  thresholds: 1%, 5%