DoH and/or DoT follow-up on resolve error about probe-engine HOT 1 CLOSED

This has also been done in github.com/ooni/netx as part of #87. Specifically, I've defined a system where specific conditions trigger automatic DoT/DoH follow-up measurements. Really, in this case, it's not even a follow-up. The measurement continues with DoT/DoH data and the results are however tagged such that the pipeline can easily understand what happened.

As mentioned in #72, it has seemed better to me not to create a manual experiment that users need to run, rather to add this functionality as part of all experiments.

For now, the trigger is a failure of the system DNS, where the receipt of bogon IP addresses, like 10.0.0.1, is also considered a failure, thus covering a common form of censorship.

from probe-engine.