When a PSR-7 request is sent using Psr18Client, the PSR-7 request protocol version is only converted to the underlying http_version option when is set to 1.0, so we cannot control that option for 1.1 or 2.0.

I have a project where I need to dynamically force the use of protocol version 1.1 but the final request is always sent using version 2.0.

This PR add option auto_upgrade_http_version to control how the request HTTP version is handled in HttplugClient and Psr18Client.

$psr18Client = $psr18Client->withOptions(['auto_upgrade_http_version' => false]);

$request = $psr18Client->createRequest()->withProtocolVersion('1.1');

// [...]

// The request will use HTTP/1.1, whereas the defaults would upgrade to 2.0
$response = $psr18Client->sendRequest($request);