data: Add hint about lock screen actions

This allows Phosh to figure out which actions should be valid on the lockscreen and hence to turn off the alarm without having to unlock the phone (see https://world.pages.gitlab.gnome.org/Phosh/phosh/app-dev.html#desktop-entry-specification).

Related xdg issue: https://gitlab.freedesktop.org/xdg/xdg-specs/-/issues/103 that will once obsolete this.

Would be great to have that in so that downstreams don't need to pick it up individually any more.