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/libraries/libwebsockets/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
       use minimal CPU and memory resources, and provide fast
       throughput in both directions.
     '';
-    homepage = https://libwebsockets.org;
+    homepage = https://github.com/warmcat/libwebsockets;
     license = stdenv.lib.licenses.lgpl21;
     platforms = stdenv.lib.platforms.all;
   };