Resolve "Encrypted DNS - RFC 8484, DNS over HTTPS, DOH (also DoT comments)"

This merge request completes the support for DNS-over-HTTP(S) built on top of nghttp2 and plugs it into BIND. Support for both GET and POST requests is present, as required by RFC8484.

Both encrypted (via TLS) and unencrypted HTTP/2 connections are supported. The latter are mostly there for debugging/troubleshooting purposes and for the means of encryption offloading to third-party software (as might be desirable in some environments to simplify TLS certificates management).

Closes #1144 (closed)