Doc: Clarify Kafka Client Support For Later Versions of Kafka Plugin

[MorrieAtElastic]

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• the Doc reference for the V10.0 Kafka Input Plugin and the V10.0 Kafka Integration Plugin both say they use the Kafka Client 2.1.0. See https://www.elastic.co/guide/en/logstash/7.5/plugins-integrations-kafka.html.

• the 9.1.0 Kafka Input Plugin states that is uses Kafka Client 2.3.0 and the changelog in the Kafka Input Plugin clearly shows a change for Kafka Client 2.3.0.

• so it is unclear as to what version of the Kafka Client the Kafka Integration Plugin does support.

• this is important because there of bug https://issues.apache.org/jira/browse/KAFKA-7755 which exists in Kafka Client 2.1.0 and is fixed in Kafka Client 2.1.1 and later client releases. See also https://archive.apache.org/dist/kafka/2.1.1/RELEASE_NOTES.html. This bug can result in situations where logstash must be stopped and restarted in order to continue receiving input from Kafka.

Can I get a clarification? Thanks