[downloader:http] add 'consume-content' option

* fix connection not being released when the response is neither
  successful nor retried
* add the ability to consume the HTTP response body instead of closing
  the connection

reference:

https://docs.python-requests.org/en/latest/user/advanced/#body-content-workflow

docs/configuration.rst

@@ -3616,6 +3616,25 @@ Description
     contains JPEG/JFIF data.
 
 
+downloader.http.consume-content
+---------------------------------
+Type
+    ``bool``
+Default
+    ``false``
+Description
+    Controls the behavior when an HTTP response is considered
+    unsuccessful
+
+    If the value is ``true``, consume the response body. This
+    avoids closing the connection and therefore improves connection
+    reuse.
+
+    If the value is ``false``, immediately close the connection
+    without reading the response. This can be useful if the server
+    is known to send large bodies for error responses.
+
+
 downloader.http.chunk-size
 --------------------------
 Type