Get rid of RW locks in the DoH code
This MR gets rid of RW locks in a hot path of the DoH code. In the original design, it was implied that we add new endpoints after the HTTP listener was created. Such a design implies some locking. We do not need such flexibility, though. Instead, we could build a set of endpoints before the HTTP listener gets created. Such a design does not need RW locks at all.
Edited by Artem Boldariev