add attic action, attic token script

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

.github/workflows/flake-update.yml

@@ -21,7 +21,12 @@ jobs:
           extra_nix_config: |
             experimental-features = nix-command flakes
           install_url: https://releases.nixos.org/nix/nix-2.19.0/install
-      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Setup Attic cache
+        uses: ryanccn/attic-action@v0
+        with:
+          endpoint: ${{ secrets.ATTIC_ENDPOINT }}
+          cache: ${{ secrets.ATTIC_CACHE }}
+          token: ${{ secrets.ATTIC_TOKEN }}
       - name: Calculate pre-drv
         run: nix ./utils/eval-to-drv.sh pre
       # - name: Pull latest docker images