Enable Drop/Create option for Dataflow Gen2

Currently the only options for DF Gen2 are to create new table, or use existing table. But during development as you update/change your dataflow, you may change your schema as well (add/drop columns, change types, etc). This currently isn't supported and requires you to manually delete the original table prior to updating the dataflow. It would be much more convenient to allow a drop/create option that will automatically drop the existing table and overwrite it with the new table schema.