Add the ability to resolve hostnames from /etc/hosts - like hosts files

[marcov]

When using AGH on a home router, it would be really useful to resolve the hostnames of the devices in the LAN.

OpenWrt based routers automatically generate a hosts file in /tmp/hosts/hosts.auto /tmp/hosts/dhcp.cfg01411c, using both static hostname provided by the user, and hostname gathered with DHCP requests.
However a.t.m. hostnames in this file cannot be resolved by AGH, limiting users ability to interact with other devices in the network without using IP addresses.

Proposed Solution

Resolve hostname from a user-specified set of hosts files.

Alternatives Considered

Have a well-known set of hosts file paths hardcoded, or editable in the yaml config file.

[ameshkov]

@marcov so would you like us to do all three?

1. /etc/hosts
2. /tmp/hosts/hosts.auto
3. DHCP (in the case if AdGuard's DHCP server is enabled)

[ameshkov]

@szolin additionally to answering A/AAAA, we should also be able to handle PTR requests, check the relevant discussion here: #1458

[szolin]

There's no /tmp/hosts/hosts.auto on our openwrt device but /tmp/hosts/dhcp.cfg01411c instead.

[marcov]

@szolin, you are right, /tmp/hosts/dhcp.cfg01411c is the right path (/tmp/hosts/hosts.auto is a custom mod I did locally).

@ameshkov that would be awesome.
Even better if for 1. and 2. you could let the user specify an arbitrary list of paths.

[ameshkov]

@szolin it seems you forgot about handling PTR