Batched deletion of objects? #188
Description
In targets, functions tar_destroy(), tar_delete(), and tar_prune() delete GCS objects one at a time. It would be great to be able to delete whole groups of objects, with version numbers whenever available. For AWS, https://www.paws-r-sdk.com/docs/s3_delete_objects/ works out really well in my case, and I implemented it in targets. Would be great to do the same for GCP. c.f. ropensci/targets#1171