bind to_device subdirective

[MayCXC]

Assistance Disclosure

No AI was used.

Adds a to_device subdirective for bind to implement #7256 without changing how addresses are parsed otherwise:

example.com {
    bind eth0 tcp4/eth1 tcp6/eth2 {
        to_device
    }
}

in the example above, the site is bound to at least three addresses. This way the tcp6/ udp6/ and ip6: networks can be used instead of a new version mode syntax, and the port is read from the site block again instead of the directive arguments.

Only one address is bound per prefix for interfaces assigned a cidr. This is preferable to composing or selecting multiple addresses to emulate a bind to device syscall; a socket manager can do that natively without the overhead of opening 2^n listeners at once, or the unreliability of trying to open the first one available iteratively. e.g. for linux, the user could apply #7342 with systemd.socket and BindToDevice/FreeBind.

Tests are todo, ideally we will mock the value of net.InterfaceByName and parse a caddyfile.

[MayCXC]

converted to draft because it shares some diffs with #7342