Provide per-partition first and last offset

[CAFxX]

The offset shell allows to dump the oldest and newest offsets currently available in a partition:
https://cwiki.apache.org/confluence/display/KAFKA/System+Tools#SystemTools-GetOffsetShell
The same information is also available from the SimpleConsumer: https://apache.googlesource.com/kafka/+/trunk/core/src/main/scala/kafka/consumer/SimpleConsumer.scala#184

This information seems to be currently missing in the data returned by kazoo-go (you can ask for the current offset of a consumergroup, but not for the per-partition oldest/newset offsets).

[kamermans]

I would also like to be able to get the partition offset details, as there seems to be no other way to compute consumer group lag with this library. I am happy to contribute but I also don't know where this information is stored in Zookeeper.

[Edit] it seems this information (first/last offset) is not stored in Zookeeper at all, and needs to be pulled from the Kafka broker. In Sarama this is done with sarama.Client.GetOffset(topic, partitionID, sarama.OffsetOldest) and sarama.Client.GetOffset(topic, partitionID, sarama.OffsetNewest).