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/nixos/www/tazj.in.nix

@@ -1,40 +0,0 @@
-# serve tazjin's website & blog
-{ depot, config, lib, pkgs, ... }:
-
-{
-  imports = [
-    ./base.nix
-  ];
-
-  config = {
-    services.nginx.virtualHosts."tazj.in" = {
-      enableACME = true;
-      forceSSL = true;
-      root = depot.users.tazjin.homepage;
-
-      extraConfig = ''
-        ${depot.users.tazjin.blog.oldRedirects}
-        location /blog/ {
-          alias ${depot.users.tazjin.blog.rendered}/;
-
-          if ($request_uri ~ ^/(.*)\.html$) {
-            return 302 /$1;
-          }
-
-          try_files $uri $uri.html $uri/ =404;
-        }
-
-        # Temporary place for serving static files.
-        location /blobs/ {
-          alias /var/lib/tazjins-blobs/;
-        }
-      '';
-    };
-
-    services.nginx.virtualHosts."git.tazj.in" = {
-      enableACME = true;
-      forceSSL = true;
-      extraConfig = "return 301 https://code.tvl.fyi$request_uri;";
-    };
-  };
-}