[fix] image_proxy: allow HTTP redirects

Without redirects the load of various images will fail when image_proxy is
enabled [1].

[1] https://github.com/searxng/searxng/pull/910#issuecomment-1045966577


Suggested-by: @dalf [1]
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>