KIP-396 — Add Reset/List Offsets Operations to AdminClient

Accepted Kafka 2.5 Admin

Adds `AdminClient.listOffsets()` (retrieve offsets by timestamp or earliest/latest/max-timestamp sentinel) and `AdminClient.deleteRecords()` (delete records up to a given offset) to the Admin API. Resetting consumer group offsets and retrieving partition offset boundaries required using the `kafka-consumer-groups.sh` CLI tool or reimplementing the low-level `ListOffsets` protocol, neither of which is suitable for programmatic use.

Details