feat(copy): add flag to create sheet if not exists

[mharrisb1]

Overview

Closes #95: Is it possible to create a sheet if it doesn't exist?

Users can now use the create_if_not_exists flag in the COPY TO command to create a sheet if it does not already exist.

copy <table_name>
to '<spreadsheet_url>'
(format gsheet, create_if_not_exists true, sheet 'Woot' );

Warning

The sheet option must also be provided. A Binder Error will be thrown if not provided

Testing

I wanted to add a note here calling out that I added unit tests but could not currently add SQL tests for this change.

To test this in the SQL tests we would need a way to programatically delete the newly created sheet and I just didn't want to mess with that right now.

We can circle back on that at a later point if we think it's necessary.