kafka: add notes about Java 7

Refs #29818.
brew-test-bot: strip bell/alert character.
percona-toolkit 2.2.8

Also add `depends_on :mysql` so mysql_config can be located.
percona-toolkit: add 2.2.8 bottle.

Closes #29868.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>