man: add ZIO_STAGE_BRT_FREE to zpool-events
And bump all the values after it, matching the header update in
67a1b037.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #14665