Make network config use  vcloud-edgegateway tools

Rather than continue to use `vcloud-net-spinner`, we should be looking to use
the
[`alphagov/vcloud-edgegateway`](https://github.com/alphagov/vcloud-edgegateway)
tool.

This means that we can specify our firewall configuration in one YAML file. This
commit adds that YAML file. It worked fine during testing.