Add feature to consider proxy-server

[frdrrhr]

Hi Eric,

I would like to request a feature for your extension. Would you please add a something, that allows to consider a proxy-server?
Something similar to simplepie/simplepie#518 and https://gist.github.com/abhij89/c7f475cd581e9af9498f4cccf7e2d9f0?

Maybe something like this in initFeedback()?

  $proxy = $GLOBALS['TYPO3_CONF_VARS']['HTTP']['proxy'] ?? null;
    if (isset($proxy) && $proxy !== '') {
        $this->feed->set_curl_options(
            array(
                CURLOPT_PROXY => $proxy
            )
        );
    }