Option to manage Captive portal

[shuvashish76]

Changing the captive portal servers is a privacy benefit and no root privileges needed.
There are presets from GrapheneOS, Kuketz and the defaults of Google.
It goes in the sprit of pdnsf privacy specific feature list.

Reference :

• https://f-droid.org/packages/io.github.muntashirakon.captiveportalcontroller/
• https://mullvad.net/en/blog/2022/10/10/android-leaks-connectivity-check-traffic