fix(out_rdkafka2): fixed a bug where it is not respecting the Buffer sections' `chunk_limit_records` and `chunk_limit_size` options

[raytung]

Fixes https://github.com/fluent/fluent-plugin-kafka/issues/462

Additionally, I just realised there's also a slight behavior change made in https://github.com/fluent/fluent-plugin-kafka/pull/454.

Prior to that commit, we were fetching Kafka topic related metadata only for the given topics, but that commit changes it such that the plugin fetches metadata for all topics. I don't think this will cause too much of an impact in production, but worth calling it out anyway.