This commit contains fixes to unit tests to make them work well on
various platforms (in particular ones shipping old versions of
OpenSSL) and for different configurations.
It also updates the generated manpage to include DoH configuration
options.
This commit completes the support for DNS-over-HTTP(S) built on top of
nghttp2 and plugs it into the 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).
This commit includes work-in-progress implementation of
DNS-over-HTTP(S).
Server-side code remains mostly untested, and there is only support
for POST requests.