String freeze exception for plasma-mobile

[Carl Schwan]

Hello,

we would like to request a string freeze exception for Plasma Mobile. 
Unfortunately a feature we added in the last release works fine on some phone 
but not all, so we added an option to disable it. This adds three strings:

- Wallpaper
- Switch homescreen and more wallpaper options
- Show wallpaper blur effect

https://invent.kde.org/plasma/plasma-mobile/-/merge_requests/444

Cheers,
Carl