support a meatadata file redirection for passthru

support a meatadata file redirection for passthru

The passthrough command provided a way to specific a metadata size, but
no way to save or set the data from a file. Provide an option so this is
allowed.

While we're here, it looks like the passthrough command only supported
file redirection for data-out commands. Go ahead and fix that with this
commit since the metadata needs to go both ways too.

Link: https://github.com/linux-nvme/nvme-cli/issues/1298
Signed-off-by: Keith Busch <kbusch@kernel.org>