feat(gs:system): steal tazjin's rebuilder script

gonna use this instead of nixos-rebuild switch, in part to get away from
global nixpkgs pins.

Change-Id: I46e2951660465790adfdf75e6e3413b5c2dfd7c7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/886
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: BuildkiteCI
Tested-by: BuildkiteCI

users/glittershark/system/system/modules/common.nix

@@ -1,5 +1,11 @@
 { config, lib, pkgs, ... }:
 
+let
+
+  depot = import ../../../../.. {};
+
+in
+
 {
   imports =
     [
@@ -35,6 +41,7 @@
     libnotify
     file
     lm_sensors
+    depot.users.glittershark.system.system.rebuilder
   ];
 
   # Some programs need SUID wrappers, can be configured further or are