KIP-218 — Make KafkaFuture.Function java 8 lambda compatible

Accepted Kafka 1.1 AdminClient

Converts `KafkaFuture.Function` and `KafkaFuture.BiConsumer` from abstract classes to `@FunctionalInterface`-annotated interfaces. As abstract classes with a single abstract method, they cannot be used with Java 8 lambda expressions, forcing users to write verbose anonymous class syntax in `AdminClient` callback code.

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