JSON output support for zpool version

This commit adds support for zpool version to output in JSON format
using '-j' option. Userland kernel module version is collected in nvlist
which is later displayed in JSON format. man page for zpool is updated.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
Closes #16217