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/base.nix

@@ -0,0 +1,36 @@
+{ config, pkgs, ... }:
+
+{
+  config = {
+    services.nginx = {
+      enable = true;
+      enableReload = true;
+
+      recommendedTlsSettings = true;
+      recommendedGzipSettings = true;
+      recommendedProxySettings = true;
+    };
+
+    # NixOS 20.03 broke nginx and I can't be bothered to debug it
+    # anymore, all solution attempts have failed, so here's a
+    # brute-force fix.
+    #
+    # TODO(tazjin): Find a link to the upstream issue and see if
+    # they've sorted it after ~20.09
+    systemd.services.fix-nginx = {
+      script = "${pkgs.coreutils}/bin/chown -f -R nginx: /var/spool/nginx /var/cache/nginx";
+
+      serviceConfig = {
+        User = "root";
+        Type = "oneshot";
+      };
+    };
+
+    systemd.timers.fix-nginx = {
+      wantedBy = [ "multi-user.target" ];
+      timerConfig = {
+        OnCalendar = "minutely";
+      };
+    };
+  };
+}