Write down policy currently used by the dir-auth group for applying changes requested by the network-health team

From time to time directory authority operators are requested to apply changes proposed by the network-health team, be it for removing relay run by operators who were doing MitM attacks or something else.

While we are still working on a proper policy to handle the different cases we are confronted with in our day-to-day network-health work it's worth writing down what directory authority operators are currently doing/having currently committed to. That could simply be the policy v0 upon which we'll build the one we are happy with.