[Bug]: KafkaIO documentation gap

[aaltay]

What happened?

There is a documentation gap when kafkaio is used in multi-language mode and one wants to pass experiment flags to the IO.

context: https://lists.apache.org/thread/c9nlm9ffrh0vtmclgflc45dp62rnoz1j

Issue Priority

Priority: 3 (minor)

Issue Components

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[jaehyeon-kim]

.take-issue