Allow to scan proxy settings #4290
Description
It should be possibly to scan a proxy url and confirm that it should be used in proxy settings.
Using DC_QR_PROXY
see
deltachat/interface#75
chatmail/core#5895
deltachat/deltachat-android#3334
Once we have a separate page for the proxy settings, it would be nice to start the qr code scanner from there also
see #4124
also related is #4231