Add testing for import/export while a backup cursor is open

Add python testing to the live import and export functionality while a backup cursor is open. The Cloud team had the following question about the interaction of import/export with backup cursors: Is it legal to run live import on a serverless instance which has a backup cursor open? As an import is really just creating a collection, the answer to this should be yes, but we do not have any testing to target this specific scenario.

Investigate if it makes sense to add similar testing to test/format, although that work does not necessarily need to be done as part of this ticket.