refactor(ops): Split //ops/nixos into different locations

Splits //ops/nixos into:

* //ops/nixos.nix - utility functions for building systems
* //ops/machines - shared machine definitions (read by readTree)
* //ops/modules - shared NixOS modules (skipped by readTree)

This simplifies working with the configuration fixpoint in whitby, and
is overall a bit more in line with how NixOS systems in user folders
currently work.

Change-Id: I1322ec5cc76c0207c099c05d44828a3df0b3ffc1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2931
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: glittershark <grfn@gws.fyi>

ops/modules/www/cl.tvl.fyi.nix

@@ -0,0 +1,30 @@
+{ config, ... }:
+
+{
+  imports = [
+    ./base.nix
+  ];
+
+  config = {
+    services.nginx.virtualHosts."cl-shortlink" = {
+      serverName = "cl";
+      extraConfig = "return 302 https://cl.tvl.fyi$request_uri;";
+    };
+
+    services.nginx.virtualHosts.gerrit = {
+      serverName = "cl.tvl.fyi";
+      serverAliases = [ "cl.tvl.su" ];
+      enableACME = true;
+      forceSSL = true;
+
+      extraConfig = ''
+        location / {
+          proxy_pass http://localhost:4778;
+          proxy_set_header  X-Forwarded-For $remote_addr;
+          # The :443 suffix is a workaround for https://b.tvl.fyi/issues/88.
+          proxy_set_header  Host $host:443;
+        }
+      '';
+    };
+  };
+}