Excessive logging from GoogleCloudStorageTransfer

In https://github.com/google/cloud-forensics-utils/blob/main/libcloudforensics/providers/gcp/internal/storagetransfer.py#L151

Currently the storage transfer client dumps the request status to the logger every 5 seconds. For transfers that take a long time, this produces a large amount of output. It might be worthwhile reducing this, perhaps looking into some kind of waiter for the transfer.