MINOR: Move `ext` block above `allprojects` block in `build.gradle` (#11741)
MINOR: Move `ext` block above `allprojects` block in `build.gradle` (#11741)

`ext` contains definitions that should be accessible in `allprojects`
(even though we don't use any right now).

Reviewers: Jason Gustafson <68c46a606457643eab92053c1c05574abb26f861@confluent.io>
TiVo/kafka,apache/kafka,TiVo/kafka,guozhangwang/kafka,lindong28/kafka,apache/kafka,guozhangwang/kafka,guozhangwang/kafka,TiVo/kafka,guozhangwang/kafka,TiVo/kafka,lindong28/kafka,apache/kafka,apache/kafka,lindong28/kafka,lindong28/kafka