Enable XFF headers for `wikiwho.wmflabs.org` and `wikiwho-api.wmcloud.org`
This is part of #wikiwho migration (T288840). The old installation at https://api.wikiwho.net has IP-based throttling. We believe that Gesis, the maintainers of the old installation, are going to advertise our installation once it's pronounced production-ready. Thus, we can expect to have a lot of outside traffic. In the spirit of the free knowledge movement, we'd like to support these consumers. With that we also want to ensure stability by throttling access by IP in the same way the old installation does.
In case you were wondering, https://wikiwho.wmflabs.org currently serves as a proxy to https://api.wikiwho.net. Once we're ready, wikiwho.wmflabs.org will be changed to point to the `wikiwho-api` instance and the old proxy instance will be deleted. In the meantime, we would like to test the throttling works under our temporary hostname at https://wikiwho-api.wmcloud.org, hence why we're asking for two hostnames to be added to the XFF headers allow list.