Add latest offsets and lag to consumer group list

[loicgreffier]

Something like:

CONSUMER GROUP   STATE    TOPIC              PARTITION  CURRENT OFFSET  END OFFSET  LAG
my-group         Stable   my-topic           0          1500            1520        20
my-group         Stable   my-topic           1          3200            3200        0
my-group         Stable   my-other-topic     0          800             850         50

This should be feasible through ConsumerGroupAsyncExecutor#getLogEndOffsets.