JSON output support for zfs version and zfs get

This commit adds support for JSON output for zfs version and zfs get
commands. '-j' flag can be used to get output in JSON format.

Information is collected in nvlist objects which is later printed in
JSON format. Existing options that work for zfs get and zfs version
also work with '-j' flag.

man pages for zfs get and zfs version are updated accordingly.

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