Make Tails Upgrader .desktop-file translatable

Currently one cannot translate “config/chroot_local-includes/usr/share/applications/tails-upgrader.desktop” through Transifex.

This desktop file is in the main Tails repository, and can easily be integrated with the existing way desktop files are translated there.

Feature Branch: feature/6489-i18n-upgrader-launcher

Parent Task: #6470

Original created by @winterfairy on 6489 (Redmine)

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