chore: add shared workflow for processing nix flake files

Signed-off-by: Dmitri Pal <[email protected]>

Author: Dmitri Pal

.github/workflows/nix-update.yml

@@ -0,0 +1,13 @@
+name: Update Nix flake
+
+on:
+  schedule:
+    - cron: "0 0 * * *"
+  workflow_dispatch:
+
+jobs:
+  nix-update:
+    permissions:
+      contents: write
+      pull-requests: write
+    uses: enarx/.github/.github/workflows/nix-update.yml@main