refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/system/system/default.nix

@@ -0,0 +1,77 @@
+args @ { depot, pkgs, ... }:
+
+rec {
+  chupacabra = import ./machines/chupacabra.nix;
+
+  chupacabraSystem = (depot.third_party.nixos {
+    configuration = chupacabra;
+  }).system;
+
+  mugwump = import ./machines/mugwump.nix;
+
+  mugwumpSystem = (depot.third_party.nixos {
+    configuration = mugwump;
+  }).system;
+
+  roswell = import ./machines/roswell.nix;
+
+  roswellSystem = (depot.ops.nixos.nixosFor ({ ... }: {
+    imports = [
+      ./machines/roswell.nix
+      "${pkgs.home-manager.src}/nixos"
+    ];
+
+    home-manager.users.grfn = { config, lib, ... }: {
+      imports = [ ../home/machines/roswell.nix ];
+      lib.depot = depot;
+      _module.args.pkgs = lib.mkForce
+        (import pkgs.path
+          (lib.filterAttrs (n: v: v != null) config.nixpkgs));
+    };
+  })).system;
+
+  yeren = import ./machines/yeren.nix;
+
+  yerenSystem = (depot.ops.nixos.nixosFor yeren).system;
+
+  iso = import ./iso.nix args;
+
+  # Build chupacabra in CI
+  meta.targets = [
+    "chupacabraSystem"
+    "mugwumpSystem"
+    "roswellSystem"
+    "yerenSystem"
+
+    "iso"
+  ];
+
+  rebuilder =
+    let
+      depotPath = "/home/grfn/code/depot";
+
+      caseFor = hostname: ''
+        ${hostname})
+          echo "Rebuilding NixOS for //users/grfn/nixos/${hostname}"
+          system=$(nix-build -E '(import ${depotPath} {}).users.grfn.system.system.${hostname}' --no-out-link)
+          ;;
+      '';
+    in pkgs.writeShellScriptBin "rebuilder" ''
+      set -ue
+      if [[ $EUID -ne 0 ]]; then
+        echo "Oh no! Only root is allowed to rebuild the system!" >&2
+        exit 1
+      fi
+
+      case $HOSTNAME in
+      ${caseFor "chupacabra"}
+      *)
+        echo "$HOSTNAME is not a known NixOS host!" >&2
+        exit 1
+        ;;
+      esac
+
+      nix-env -p /nix/var/nix/profiles/system --set $system
+      $system/bin/switch-to-configuration switch
+    '';
+}