The zilstat command has no man page. Add zilstat.1 documenting all
options and field definitions based on the source in cmd/zilstat.in.
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Christos Longros <chris.longros@gmail.com>
Closes#18303
