refactor(users/multi): make my user directory CI-compatible.

My home-manager config is not currently readTree compatible, which means
that it's not built by CI. This constructs a house of cards around
home-manager to make this buildable in CI.

Change-Id: I80480f24ff47347f46d708edbbf34d59fa76adac
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2123
Tested-by: BuildkiteCI
Reviewed-by: multi <depot@in-addr.xyz>

users/multi/home/default.nix

@@ -0,0 +1,27 @@
+{ depot, pkgs, lib, ... }:
+
+let
+  nixpkgs = import pkgs.nixpkgsSrc {};
+  home-modules = import "${nixpkgs.home-manager.src}/modules";
+  outerLib = lib;
+
+  home = path:
+    let 
+      configSet = import path { inherit depot pkgs; };
+    in
+      home-modules {
+        pkgs = nixpkgs;
+        configuration = { config, lib, ... }: (
+          {
+            _module.args.pkgs = outerLib.mkForce (import pkgs.nixpkgsSrc {});
+          } // configSet
+        );
+      };
+
+in
+  rec {
+    whitby = home ./configs/whitby.nix;
+    whitbyHome = whitby.activationPackage;
+
+    meta.targets = [ "whitbyHome" ];
+  }