zpool/zfs: Add '-a|--all' option to scrub, trim, initialize

Add support for the '-a | --all' option to perform trim,
scrub, and initialize operations on all pools.
Previously, specifying a pool name was mandatory for
these operations. With this enhancement, users can now
execute these operations across all pools at once,
without needing to manually iterate over each pool
from the command line.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Akash B <akash-b@hpe.com>
Closes #17524