[meta] DNS testing in reforis

This issue is related to our meeting about better DNS diagnostic

check_connection script should be replaced with python version which could test other DNS settings (forwarding not working, DNS hijack etc.)

This script can use some functionality from resolver_rpcd (see https://pypi.org/project/ubus/ and README.md) and read setting from uci https://gitlab.labs.nic.cz/turris/pyuci resolver configuration

Related issues/MR:

• pytest-xdist MR https://gitlab.nic.cz/turris/turris-os-packages/-/issues/317 / https://github.com/openwrt/packages/pull/13010
• https://gitlab.nic.cz/turris/turris-os-packages/-/issues/620
• augeas MR https://github.com/openwrt/packages/pull/12913
• Deckard MR https://gitlab.nic.cz/turris/turris-os-packages/-/merge_requests/460

cc @pspacek @kkoci