daemon: track dhcp and reconfigure as validating stub / resolver

[vavrusa]

There should be a module to track changes in the network and environment to detect when the resolver is in an:

• Environment that blocks DNS queries altogether (and revert to stub mode)
• Environment with DNSSEC-unaware resolver (do validation)
• Open environment (full recursive resolver)

This would make it as painless as possible for the end users with frequent network transitions (hotel wifi, workplace, home, ...)

[vavrusa]

Fallback to https://github.com/fcambus/rrda if the DNS is filtered/unreachable.

[pspacek]

Moved to https://gitlab.labs.nic.cz/knot/knot-resolver/issues/244, closing.