Impossible to create docker network with --ipv6

hi,

try to run the self-hosted runner on IPv6 only system. Runner runs fine on the system and connected thanks to nat64 to github.
Docker config on the host:

{
"ipv6": true,
"ip6tables": true,
"experimental": true,
"fixed-cidr-v6": "fd00::/64",
"default-address-pools": [
    { "base": "172.17.0.0/16", "size": 16 },
    { "base": "172.18.0.0/16", "size": 16 },
    { "base": "172.19.0.0/16", "size": 16 },
    { "base": "172.20.0.0/14", "size": 16 },
    { "base": "172.24.0.0/14", "size": 16 },
    { "base": "172.28.0.0/14", "size": 16 },
    { "base": "192.168.0.0/16", "size": 20 },
    { "base": "fd01::/64", "size": 112 }
  ]
}

But all container networks created via action runner are always without IPv6. See your code:

      public async Task<int> DockerNetworkCreate(IExecutionContext context, string network)
        {
#if OS_WINDOWS
            return await ExecuteDockerCommandAsync(context, "network", $"create --label {DockerInstanceLabel} {network} --driver nat", context.CancellationToken);
#else
            return await ExecuteDockerCommandAsync(context, "network", $"create --label {DockerInstanceLabel} {network}", context.CancellationToken);
#endif

There is no possible way to inject --ipv6 to it.
Docker has no config flag to enable it by default

Solution add a config option to enable ipv6 on network create.

Start at the DockerNetworkCreate method shown in the issue and trace how runner configuration options are defined and passed to Docker network creation. Add a configurable IPv6 setting whose enabled behavior results in network creation with IPv6 support, and verify the resulting command and configuration handling with the runner's existing tests.