normalize the start time to the beginning of the month in export api

vault/activity_log.go

@@ -2971,6 +2971,9 @@ func (a *ActivityLog) writeExport(ctx context.Context, rw http.ResponseWriter, f
 	}
 	defer a.inprocessExport.Store(false)
 
+	// Normalize the start time to the beginning of the month to keep consistency with the sys/counters API
+	startTime = timeutil.StartOfMonth(startTime)
+
 	// Find the months with activity log data that are between the start and end
 	// months. We want to walk this in cronological order so the oldest instance of a
 	// client usage is recorded, not the most recent.