This commit makes sending HTTP/3 request with nghttp3 work. It
minimally receives HTTP response and calls nghttp3 callbacks, but no
processing is made at the moment.
Closes#4215
USe configure --with-ngtcp2 or --with-quiche
Using either option will enable a HTTP3 build.
Co-authored-by: Alessandro Ghedini <alessandro@ghedini.me>
Closes#3500