add redirect to catch removed Nix manual page

page removed in NixOS/nix#7972

Requesting a pull to NixOS:master from fricklerhandwerk:manual-amazon-redirect

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netlify.toml

@@ -142,6 +142,12 @@
   status = 302
   force = true
 
+[[redirects]]
+  from = "/manual/nix/:version/package-management/s3-substituter*"
+  to = "/manual/nix/:version/command-ref/conf-file.html#conf-substituters"
+  status = 302
+  force = true
+
 [[redirects]]
   from = "/manual/nixpkgs"
   to = "/manual/nixpkgs/stable"