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/compilers/elm/packages/elm.nix

@@ -25,7 +25,7 @@ mkDerivation {
     snap-server template-haskell text time unordered-containers
     utf8-string vector zip-archive
   ];
-  homepage = "http://elm-lang.org";
+  homepage = "https://elm-lang.org";
   description = "The `elm` command line interface";
   license = stdenv.lib.licenses.bsd3;
 }