unbound: try to get closer to upstream version
Our version of unbound package is quite different from upstream version ( https://github.com/openwrt/packages/tree/master/net/unbound )
- Configuration is shipped via resolver-conf package https://gitlab.labs.nic.cz/turris/turris-os-packages/tree/test/net/resolver-conf
- Root key is in dnssec-rootkey https://gitlab.labs.nic.cz/turris/turris-os-packages/tree/test/net/dnssec-rootkey
We could try to follow config option from https://github.com/openwrt/packages/blob/master/net/unbound/files/unbound.uci in resolver-conf unbound section. So it's not so confusing for users from openwrt.