Add support for AdminAPI `DescribeCluster()` and `DescribeTopics()`

[Desmond Kirrane]

I'm looking for the rust equivalent of the Java org.apache.kafka.clients.admin.AdminClient API

            adminClient
                .describeCluster(
                    new DescribeClusterOptions()
                        .timeoutMs((int) Math.min(Integer.MAX_VALUE, remainingWaitMs)))
                .nodes()
                .get();

and

        adminClient.describeTopics(
            topicNames, new DescribeTopicsOptions().timeoutMs(Math.toIntExact(timeoutMs)));

It looks like it's available in librdkafka now via this commit
https://github.com/confluentinc/librdkafka/pull/4240/files