Add captive portal detection

[smarek]

Currently, when Unbound is enabled, captive portals are not detected, and in case wifi AP intercepts DNS communication, there is no indication.

• [ ] Detect captive portals
• [ ] Add notification about captive portals
• [ ] Enable temporarily disable unbound to auth to captive portal or add current DHCP provided DNS server as insecure root resolver

[smarek]

ad https://www.chromium.org/chromium-os/chromiumos-design-docs/network-portal-detection

[pspacek]

FYI it seems that you are going to re-implement dnssec-trigger :-) You might be interested in https://www.nlnetlabs.nl/projects/dnssec-trigger/

I hope this helps.