treewide: Change URLs to HTTPS

Lots of URLs were HTTP redirect to HTTPS. Changed those and checked them
if there's actual content. Inspired by
https://github.com/NixOS/nixpkgs/issues/60004

pkgs/development/python-modules/djangorestframework/default.nix

@@ -15,7 +15,7 @@ buildPythonPackage rec {
 
   meta = with stdenv.lib; {
     description = "Web APIs for Django, made easy";
-    homepage = http://www.django-rest-framework.org/;
+    homepage = https://www.django-rest-framework.org/;
     maintainers = with maintainers; [ desiderius ];
     license = licenses.bsd2;
   };