Add content-type header for requestOptions

[miramir]

In PHP 7.2.25

I see notice: "Notice: fopen(): Content-type not specified assuming application/x-www-form-urlencoded"

ErrorException: Notice: fopen(): Content-type not specified assuming application/x-www-form-urlencoded
#8 /var/www/td/vendor/yiisoft/yii2-httpclient/src/StreamTransport.php(61): yii\httpclient\StreamTransport::send
#7 /var/www/td/vendor/yiisoft/yii2-httpclient/src/Client.php(233): yii\httpclient\Client::send
#6 /var/www/td/vendor/yiisoft/yii2-httpclient/src/Request.php(444): yii\httpclient\Request::send
#5 /var/www/td/vendor/kak/clickhouse/Command.php(150): kak\clickhouse\Command::execute
#4 /var/www/td/components/ChTarget.php(104): app\components\ChTarget::export
#3 /var/www/td/components/ChTarget.php(134): app\components\ChTarget::collect
#2 /var/www/td/vendor/yiisoft/yii2/log/Dispatcher.php(191): yii\log\Dispatcher::dispatch
#1 /var/www/td/vendor/yiisoft/yii2/log/Logger.php(177): yii\log\Logger::flush
#0 internal: null