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Update all headers in the "zpool list" examples in the ZFS chapter to display

Description

Update all headers in the "zpool list" examples in the ZFS chapter to display
all columns that are currently available.
In particular, CKPOINT, EXPANDSZ, and FRAG were added and set with sensible
defaults for the example.

Reviewed by: sevan@
Differential Revision: https://reviews.freebsd.org/D16834