String freeze exception for plasma-nm

[Nicolas Fella]

Hi,

I made some changes to plasma-nm to improve the way it handles importing
VPN connections. In particular I improved what happens when importing
fails, by showing an error message to the user instead of (mostly)
silently failing.

I'd consider this a somewhat important UX improvement and thus would
like to ship that with Plasma 5.27, but it involves some new strings.
I'd argue that showing a potentially untranslated error message is
better than showing no error at all, so adding the strings shouldn't harm.

The relevant MRs are:

- https://invent.kde.org/plasma/plasma-nm/-/merge_requests/224

- https://invent.kde.org/plasma/plasma-nm/-/merge_requests/230

Cheers

Nico