docs: ja_JP/howto: Catch up update in v6.8

Catch up the update made in commit e49ad8530de9 ("CREDITS, MAINTAINERS,
docs/process/howto: Update man-pages' maintainer").

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Tsugikazu Shibata <shibata@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240502085610.111739-1-akiyks@gmail.com

docs: Move ja_JP/howto.rst to ja_JP/process/howto.rst

Let Japanese translation of howto.rst in the language drop-down list
by moving it to the expected place.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Tsugikazu Shibata <shibata@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <b175c52f-34ee-4753-b172-e57fee6fcc30@gmail.com>