Feature request: support docker execution with an IPv6 network

With the following `/etc/docker/daemon.json` file, I'm able to get the output below indicating that an IPv6 address is available.

### `/etc/docker/daemon.json`
```json
{
"ipv6": true,
"fixed-cidr-v6": "2001:db8:1::/64"
}
```

```
❯ docker run -it archlinux:latest ip addr | grep inet
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
inet 172.17.0.2/16 brd 172.17.255.255 scope global eth0
inet6 2001:db8:1::242:ac11:2/64 scope global nodad
inet6 fe80::42:acff:fe11:2/64 scope link tentative
```

However, if I run a test which implements this project, executing `ip addr` in the container does not yield an IPv6 address.

```
❯ docker exec -it ffb07eaee33b ip addr | grep inet
inet 127.0.0.1/8 scope host lo
inet 172.23.0.5/16 brd 172.23.255.255 scope global eth0
```

Perhaps there is a flag we can add to indicate that docker should execute with an IPv6 address.

The issue does not name files or tests; start by tracing how this project creates Docker containers and where network options are configured. Reproduce the IPv6 setup described above, then verify that the project's test container exposes an IPv6 address with `ip addr`.

Written by the indexing model from the issue text.