Write a background hook that induces lag between 1) lastApplied and lastWritten and 2) lastWritten and lastDurable.

We use the stopReplProducer in many tests that require pauses in replication. We should consider adding more granular failpoints to pause oplog writing, oplog application, and increase the journal flushing interval seconds to control the drift between lastApplied and lastWritten, and lastWritten and lastDurable.