Add script for updating local translation files

* packages/gen-local-l10n.sh: New.

This script can be used to update the local_l10n files we have for a few
KDE packages and a few languages. To use the script you need some
scripts from https://invent.kde.org/sysadmin/l10n-scripty and
https://invent.kde.org/sdk/kde-dev-scripts.

• GnuPG-bug-id: T7489