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/tools/networking/gandi-cli/default.nix

@@ -19,7 +19,7 @@ buildPythonApplication rec {
 
   meta = with stdenv.lib; {
     description = "Command-line interface to the public Gandi.net API";
-    homepage = http://cli.gandi.net/;
+    homepage = https://cli.gandi.net/;
     license = licenses.gpl3Plus;
     maintainers = with maintainers; [ ckampka ];
   };