fix(logx): log when an operation is starting

Not logging when an operation is starting complicates reasoning
about how much time it took to fail, which is something that caused
issues investigating ooni/probe#2544.

internal/logx/operation.go

@@ -27,6 +27,7 @@ func newOperationLogger(maxwait time.Duration, logger model.Logger, format strin
 		wg:      &sync.WaitGroup{},
 	}
 	ol.wg.Add(1)
+	ol.logger.Infof("%s... started", ol.message)
 	go ol.maybeEmitProgress()
 	return ol
 }