Admin client: list offsets per topic/partition

[noamta-gloat]

Describe the solution you'd like
A new function in the admin client that lets me retrieve the offsets (earliest/latest) of each partition.

Additional context
Confluent's admin client has list_offsets.

My use case is retrieving the number of messages behind per consumer-group/topic. list_consumer_group_offsets provides the offsets per consumer group, and I need the offset of the latest messages.