[SPARK-3719][CORE]:"complete/failed stages" is better to show the total ...

...number of stages
@uncleGen The web UI only remembers information on a fixed number of stages in order to limit its memory usage, so it's possible that the displayed number of completed stages will be much higher than the number of rows displayed in the stage table.  I think Reynold's suggestion was to make this more explicit by adding "(only showing yy)" to emphasize that some garbage-collected stage information ins't being displayed.