Close#1843
Squashed commit of the following:
commit cc82b373816b76a803d29e4baae18384aa0f8c67
Author: Simon Zolin <s.zolin@adguard.com>
Date: Thu Aug 20 14:20:35 2020 +0300
* /control/dns_config: allow all valid bootstrap server notations
* use dnsproxy v0.31.1