ci(flake): add update-flake-lock github action

.github/workflows/update-flake-lock.yml

@@ -0,0 +1,27 @@
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - name: Update flake.lock
+        uses: DeterminateSystems/update-flake-lock@main
+        with:
+          pr-title: "Update flake inputs" # Title of PR to be created
+          pr-labels: |                  # Labels to be set on the PR
+            dependencies
+            automated
+          git-author-name: 'Pantheon'
+          git-author-email: 'github-actions[bot]@users.noreply.github.com'
+          git-committer-name: 'Pantheon'
+          git-committer-email: 'github-actions[bot]@users.noreply.github.com'
+          pr-assignees: ${{ github.repository_owner }}
+          pr-reviewers: ${{ github.repository_owner }}