R6CG

Re-add use-application-dns.net - explicit signal for DNS filtering

1

With the news that [Firefox plans to start enabling ECH](https://groups.google.com/a/mozilla.org/g/dev-platform/c/uv7PNrHUagA/m/BNA4G8fOAAAJ) in the next releases, I wanted to suggest people check censorship measurements for [use-application-dns.net](https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet), because that canary domain is meant...