As we saw in SERVER-50626, we must enable rsSyncApplyStop in a specific way to avoid a race condition. Let's audit all our tests and ensure they use the utility functions in write_concern_util.js instead of enabling rsSyncApplyStop directly.

Also, the code in write_concern_util.js currently waits for a specific log message to know that the oplog fetcher has reached the rsSyncApplyStop failpoint. Let's use the modern waitForFailPoint command in write_concern_util.js instead.