Adding new read-only compatible zpool features to compatibility.d/grub2

GRUB2 is compatible with all "read-only compatible" features,
so it is safe to add new features of this type to the grub2
compatibility list. We generally want to include all compatible
features, to minimize the differences between grub2-compatible
pools and no-compatibility pools.

Adding new properties livelist and zpool_checkpoint accordingly.

Also adding them to the man page which references this file as an
example, for consistency.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Colm Buckley <colm@tuatha.org>
Closes #14893