MINOR: Add upgrade guide for KAFKA-8421 (#7925)
MINOR: Add upgrade guide for KAFKA-8421 (#7925)

Co-Authored-By: A. Sophie Blee-Goldman <1e61562ba755b577a573aede358e8d138a7bbc05@gmail.com>

Reviewers: A. Sophie Blee-Goldman <1e61562ba755b577a573aede358e8d138a7bbc05@gmail.com>
sslavic/kafka,guozhangwang/kafka,Chasego/kafka,apache/kafka,sslavic/kafka,apache/kafka,lindong28/kafka,apache/kafka,TiVo/kafka,lindong28/kafka,guozhangwang/kafka,TiVo/kafka,Chasego/kafka,lindong28/kafka,Chasego/kafka,TiVo/kafka,sslavic/kafka,lindong28/kafka,guozhangwang/kafka,sslavic/kafka,TiVo/kafka,Chasego/kafka,guozhangwang/kafka,apache/kafka