libnetwork: support custom DNS servers in Windows overlay driver

[olljanat]

- What I did
Decision in #19474 seems to be that there is no option to disable embedded DNS but user can provide own DNS servers with --dns option. However that logic does not exist in Windows version of overlay driver so I fixed that.

- How I did it
Copy & paste logic from non-overlay driver:

moby/daemon/libnetwork/drivers/windows/windows.go

Line 732 in 663aa7a

endpointStruct.DNSServerList = strings.Join(epOption.DNSServers, ",")

- How to verify it
Create attachable test network:

docker network create --driver overlay --attachable test

Start test container:

docker run -it --rm --network=test --dns=1.1.1.1 mcr.microsoft.com/windows/nanoserver:ltsc2025

NOTE! In Windows, gateway is always first DNS server inside of the container but internally DNS server(s) provided by user are used. That can be confirmed by testing with both valid and invalid DNS server IP addresses.

- Human readable description for the release notes

- The Windows overlay network driver now supports option `--dns`.

[robmry]

At the moment, it looks we just ignore options like com.docker.network.endpoint.macaddress in this case ... after this change we'll return an error if those options are malformed, then still ignore them. Which might be even more confusing/annoying?

Maybe it'd be marginally better to continue ignoring those other options, by splitting a ParseDNSServers out of parseEndpointOptions and calling that from here?

[robmry]

LGTM - thank you.

[thaJeztah]

@robmry do we need a change-log entry for this one? (Also not sure if there's docs mentioning "doesn't work on Windows")

[robmry]

@robmry do we need a change-log entry for this one? (Also not sure if there's docs mentioning "doesn't work on Windows")

I don't see any docs to be updated, I've added a release note.

[thaJeztah]

LGTM