adguardhome: Implement initial package recipe

AdGuardHome is a network-wide ads and trackers blocking DNS server.
After installing it with opkg, start it like every service:
/etc/init.d/adguardhome start

In order to complete the installation vist http://{YOUR_ROUTERS_IP}:3000.

Then you can setup dnsmasq to forward DNS traffic to AdGuardHome:
uci -q delete dhcp.@dnsmasq[0].server
uci add_list dhcp.@dnsmasq[0].server=127.0.0.1#{PORT_SET_DURING_INSTALL}
uci set dhcp.@dnsmasq[0].noresolv=1
uci commit dhcp
/etc/init.d/dnsmasq restart

Signed-off-by: Dobroslaw Kijowski <dobo90@gmail.com>