HTTP CONNECT method is now supported in HTTP/1 connections.  It's disabled
in all currently existing standard modules.  A new variable $port is added
that contains the port passed by client in HTTP CONNECT.  The $host
variable contains the host part.

A new module ngx_http_tunnel module is added which establishes a tunnel
to a backend.  It supports the newly added HTTP CONNECT method and can be
used to set up an HTTP CONNECT proxy.

As recommended by RFC 9110, proxy target should be restricted to ensure
safe proxying:

: Proxies that support CONNECT SHOULD restrict its use to a limited set
: of known ports or a configurable list of safe request targets.

Example config:

    server {
        listen 8000;

        resolver dns.example.com;

        map $port $tun_port {
            80             1;
            443            1;
        }

        map $host $tun_host {
            hostnames;

            example.com    1;
            *.example.org  1;
        }

        map $tun_port$tun_host $tun {
            11             $host:$port;
        }

        location / {
            tunnel_pass $tun;
        }
    }

Request:

    $ curl -px 127.0.0.1:8000 http://example.com

Added ngx_openssl_cache_module, which indexes a type-aware object cache.
It maps an id to a unique instance, and provides references to it, which
are dropped when the cycle's pool is destroyed.

The cache will be used in subsequent patches.

Based on previous work by Mini Hawthorne.

The module allows to pass connections from Stream to other modules such as HTTP
or Mail, as well as back to Stream.  Previously, this was only possible with
proxying.  Connections with preread buffer read out from socket cannot be
passed.

The module allows selective SSL termination based on SNI.

    stream {
        server {
            listen 8000 default_server;
            ssl_preread on;
            ...
        }

        server {
            listen 8000;
            server_name foo.example.com;
            pass 127.0.0.1:8001; # to HTTP
        }

        server {
            listen 8000;
            server_name bar.example.com;
            ...
        }
    }

    http {
        server {
            listen 8001 ssl;
            ...

            location / {
                root html;
            }
        }
    }

Although it has better implementation status than HTTP/3 server push,
it remains of limited use, with adoption numbers seen as negligible.
Per IETF 102 materials, server push was used only in 0.04% of sessions.
It was considered to be "difficult to use effectively" in RFC 9113.
Its use is further limited by badly matching to fetch/cache/connection
models in browsers, see related discussions linked from [1].

Server push was disabled in Chrome 106 [2].

The http2_push, http2_push_preload, and http2_max_concurrent_pushes
directives are made obsolete.  In particular, this essentially reverts
7201:641306096f5b and 7207:3d2b0b02bd3d.

[1] https://jakearchibald.com/2017/h2-push-tougher-than-i-thought/
[2] https://chromestatus.com/feature/6302414934114304

The change allows to compile QUIC with OpenSSL which lacks BoringSSL QUIC API.

This implementation does not support 0-RTT.

Previously, QUIC used the existing UDP framework, which was created for UDP in
Stream.  However the way QUIC connections are created and looked up is different
from the way UDP connections in Stream are created and looked up.  Now these
two implementations are decoupled.

ngx_http_v2_huff_decode.c and ngx_http_v2_huff_encode.c are renamed
to ngx_http_huff_decode.c and ngx_http_huff_encode.c.

Renamed and removed some macros.