Add new query type QUERY_EXTERNAL_BLOCKED

[DL6ER]

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Add new query type QUERY_EXTERNAL_BLOCKED triggered by an NXDOMAIN response with set AD bit. This is how Quad9 signals a blocked domain as suggested here (this behavior has been confirmed in private communication).

The web interface needs to be adapted to acknowledge this new query type in a follow-up PR on the AdminLTE repo.

This template was created based on the work of udemy-dl.

[AzureMarker]

Is this a standard practice, or only implemented by Quad9?

[DL6ER]

I'm not aware of any other freely available DNS provider that does itself blocking where I could test this.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/seeing-upstream-null-results-non-changeable/12539/2