Teradata - add support for CURRENT_TIMESTAMP

natejgardner

The Dataiku formula language now() function hooks into many databases' syntax for returning the current time, but doesn't currently support Teradata, limiting the ability to use Dataiku formula language in Teradata across many recipes for date-related calculations. By adding support for CURRENT_TIMESTAMP/CURRENT_DATE, common use cases like filter diff(my_date,now(),'d') > 0 will become possible, making it easy to create useful time windows and take advantage of other convenient Dataiku formula language features without needing to write SQL.