[downloader:http] support using a different method than GET (#2433)

by setting the '_http_method' metadata field for a file

gallery_dl/downloader/http.py

@@ -120,9 +120,9 @@ class HttpDownloader(DownloaderBase):
             # connect to (remote) source
             try:
                 response = self.session.request(
-                    "GET", url, stream=True, headers=headers,
-                    timeout=self.timeout, verify=self.verify,
-                    proxies=self.proxies)
+                    kwdict.get("_http_method", "GET"), url,
+                    stream=True, headers=headers, timeout=self.timeout,
+                    verify=self.verify, proxies=self.proxies)
             except (ConnectionError, Timeout) as exc:
                 msg = str(exc)
                 continue