MINOR: Mention in configuration of broker setting log.retention.ms that -1 disables retention by time (#6464)
MINOR: Mention in configuration of broker setting log.retention.ms that -1 disables retention by time (#6464)

Includes an update to the relevant configuration doc.
guozhangwang/kafka,lindong28/kafka,sslavic/kafka,apache/kafka,TiVo/kafka,sslavic/kafka,TiVo/kafka,lindong28/kafka,apache/kafka,Chasego/kafka,sslavic/kafka,guozhangwang/kafka,TiVo/kafka,KevinLiLu/kafka,sslavic/kafka,KevinLiLu/kafka,guozhangwang/kafka,apache/kafka,Chasego/kafka,Chasego/kafka,TiVo/kafka,Chasego/kafka,KevinLiLu/kafka,noslowerdna/kafka,lindong28/kafka,lindong28/kafka,KevinLiLu/kafka,guozhangwang/kafka,apache/kafka,noslowerdna/kafka,noslowerdna/kafka,noslowerdna/kafka