* Include fields date_paid and date_completed to wp_wc_order_stats
TODO: add script to create new columns in the database
* Add update script and new columns in get_schema
* Add new configuration in Analytics > Settings to configure type of date used in Revenue report
* Change date_column_name to date_paid
TODO: This will be configurable in future
* Add date type config field
* Use customizable date field in DataStore
* Change label
* Fix linter errors
* Remove blank line
* Put default column name back to date_created
* Make date_paid and date_completed nullable to help with unit tests
* Remove new table creation in update function and use query method instead of get_var
* Extend stats constructor
* Improve date type configuration description
* Set date column name default to date_created to test if build passes
* Fix phpcs issue on constructor
* Remove cache bypass added by mistake
* Improve changelog
* Fill date_paid and date_completed for refunds to avoid problems whem they are being used to sort
Fix unit tests when date_paid or date_completed are being used as sort date
* Change default to date_created
* Bump update script to 7.5.0
* Add prefix and postmeta variables for script
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