Right now we synchronously insert one document into the DLQ at a time, we should move the i/o work to a background thread and make all inserts into the DLQ async. The worker thread should push all documents destined for the DLQ into a queue that the DLQ background thread is constantly consuming from.

Ideally the work we do here can be reused to do something similar in the merge operator.

Slack context: https://mongodb.slack.com/archives/C05P740L0VC/p1694540160003889