add OpenWRT Makefile

[honwen]

docs: https://openwrt.org/docs/guide-developer/packages

[ameshkov]

Tbh, I am not fully sure about the service part.

Wouldn't it be better to implement #39 using kardianos/service (just like we do in AdGuard Home), and reuse it?
Also, I think that implementing dnsproxy configuration should be done prior to this task.

[honwen]

As Said in AdguardTeam/AdGuardHome#1348, kardianos/service does not match the initscripts standard of openwrt, and openwrt require a makefile to add preinstalled packages to the final image.

[ameshkov]

@honwen sure, and here's what we do in AGH to handle this:
https://github.com/AdguardTeam/AdGuardHome/blob/master/internal/home/service.go#L456

Search for util.IsOpenWRT there to see the necessary changes.

[dhewg]

This is an OpenWRT package, it doesn't belong here.
But the package has been added already: openwrt/packages#16130

On the good side, while this one downloaded a binary release, the merged package compiles the go sources.
But the merged one doesn't ship a init/uci config yet, while this one does.

@honwen / @1715173329 maybe you're interested to get that merged?

[1715173329]

@dhewg I just made a basic init script, please make a test/review if you are free ;)
https://github.com/immortalwrt/packages/blob/master/net/dnsproxy/files/dnsproxy.config
https://github.com/immortalwrt/packages/blob/master/net/dnsproxy/files/dnsproxy.init

[dhewg]

Nice! There're a few small things I'd change, but it's not up to me ;)
Let's discuss that in a openwrt/packages PR so other reviewers will see that too!