log WiredTiger record store oplog processing times persistent between versions

In MongoDB versions prior to 4.4, we were printing:

WiredTiger record store oplog processing took

In MongoDB versions post 4.4, we print:

WiredTiger record store oplog processing finished

It would be helpful to keep such startup messages consistent and identical between versions, otherwise searching for the exact string does not provide the output for all MongoDB versions.

I also think "finished" is a less acceptable word in terms of time tracking unless we also print "started"