Redefine statistics callback

[mr-swifter]

librdkafka provides statistics over a callback which can be set using rd_kafka_conf_set_stats_cb.

Statistics callback should be set in combination with statistics.interval.ms.

Reference https://docs.confluent.io/platform/current/clients/librdkafka/html/md_STATISTICS.html

https://quicktype.io can be used to generate proper structs for statistics content.

[blindspotbounty]

@felixschlegel, @FranzBusch I have made some approach for this improvement.
Unfortunately, I have some doubts regarding ideas in the original code, so could you give me a piece of advise in the PR, please?