Deprecate ruby-kafka version

### Is your feature request related to a problem? Please describe.

https://github.com/zendesk/ruby-kafka is no longer active.
So, I think It would be better to recommend using rdkafka instead of ruby-kafka version.

And, It seems that there are cases where you cannot connect to the broker when using ruby-kafka.
Ref. https://github.com/fluent/fluent-plugin-kafka/issues/483

### Describe the solution you'd like

When using ruby-kafka, it shows a message recommending rdkafka, etc.

### Describe alternatives you've considered

TBD

### Additional context

_No response_

No file or test is named. Start by locating the plugin configuration path that selects ruby-kafka, inspect existing tests for that path, and define completion as showing a recommendation for rdkafka when ruby-kafka is selected without changing other broker behavior.

Written by the indexing model from the issue text.