Ruby examples are based on abandoned library instead of rdkafka-ruby that is a binding to librdkafka

The Ruby examples provided in this repository are based on an outdated and no longer maintained library, rather than using rdkafka-ruby, which is a more current and actively supported binding to librdkafka.

The ruby-kafka repo clearly states:

> This library is no longer actively developed and has been superseded by [librdkafka](https://github.com/edenhill/librdkafka) via [rdkafka-ruby](https://github.com/appsignal/rdkafka-ruby/) bindings. While this library may still receive security patches and bug fixes, it is no longer recommended for production usage.