fix(monorepo-gerrit): Configure nginx reverse proxy correctly

Configures the reverse-proxy as per Gerrit's documentation at
https://gerrit-review.googlesource.com/Documentation/config-reverseproxy.html

ops/nixos/camden/default.nix

@@ -411,6 +411,8 @@ in lib.fix(self: {
       extraConfig = ''
         location / {
           proxy_pass http://localhost:4778;
+          proxy_set_header  X-Forwarded-For $remote_addr;
+          proxy_set_header  Host $host;
         }
       '';
     };