Support "protocol_version" stream context option for proxy connections

Description

Hello. We have protocol_version option for talking with remote host using specified HTTP protocol version. However, HTTP connection to proxy always goes with HTTP/1.0 which upsets my proxy server.

Example:

<?php
$ctx = stream_context_create(
  ['http' => ['proxy' => 'tcp://corporate-proxy.example:3128']]
);
echo file_get_contents("https://getcomposer.org/versions", false, $ctx);

Result:

Warning: file_get_contents(): SSL: Connection reset by peer in a.php on line 5

Warning: file_get_contents(https://getcomposer.org/versions):
  Failed to open stream: Cannot connect to HTTPS server through proxy in a.php on line 5

Actual request as seen by wireshark:

CONNECT getcomposer.org:443 HTTP/1.0

HTTP/1.1 426 Upgrade Required
date: Mon, 20 Jun 2022 10:23:30 GMT
server: envoy
connection: close
content-length: 0

My proxy server supports only HTTP/1.1. So it's would be very handy to have an option for configuring http protocol version for proxy connections.

PHP の HTTP ストリームラッパーとプロキシ CONNECT リクエストのパスから始め、直接リクエストに対する既存の protocol_version の処理と比較します。このオプションがプロキシ接続に適用されることを確認し、HTTPS-through-proxy の例を実行して、CONNECT リクエストが設定された HTTP バージョンを使用することを確認します。