Add workflow for upgrading locales to next year

Schedule workflow to run on 1st of August of each year
* Calculate data for all present locales for the next year
* Add news item to website
* Build and deploy page after upgrade

.github/workflows/upgrade-year.yml

@@ -0,0 +1,166 @@
+name: Upgrade year
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 0 1 8 *'
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  upgrade-year:
+    runs-on: ubuntu-latest
+    concurrency:
+      group: "update-locales"
+      cancel-in-progress: false
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Determine next year
+        id: get-next-year
+        run: |
+          current_year=$( date +'%Y' )
+          echo "year=$(( current_year + 1 ))" >> "${GITHUB_OUTPUT}"
+
+      - name: Set up Python environment
+        run: |
+          python -m venv /tmp/venv
+          /tmp/venv/bin/pip install --upgrade pip
+          /tmp/venv/bin/pip install holidata
+
+      - name: Upgrade locales years
+        id: upgrade-year
+        run: |
+          year="${{ steps.get-next-year.outputs.year }}"
+          formats=( "json" "yaml" "xml" "csv" )
+          
+          for locale_dir in holidata/??-?? ; do
+            locale="${locale_dir/holidata\//}"
+            echo "Generating locale '${locale}' files for ${year}..."
+
+            for format in "${formats[@]}" ; do
+              echo "Generating ${locale}/${year}.${format}"
+              /tmp/venv/bin/holidata --year="${year}" --locale="${locale}" --output="${format}" > "${locale_dir}/${year}.${format}"
+            done
+          
+            echo "Generated locale ${locale} for year ${year}"
+            echo "${locale##*-}" >> /tmp/countries
+          done
+
+          sort -u < /tmp/countries > /tmp/sorted
+          countries="$( paste -s -d, /tmp/sorted )"
+          echo "countries=${countries//,/, }" >> "${GITHUB_OUTPUT}"
+          current_date="$( date +'%Y-%m-%d' )"
+          cat <<EOF > "content/news/${current_date}-holidata-${year}.md"
+          ---
+          title: "Holidata for ${year} available"
+          date: ${current_date}T00:00:00+02:00
+          layout: "news_item"
+          ---
+          
+          The holidata for ${year} is now available for all locales!
+          <!--more-->
+          We have published the holiday data set for ${year}.
+          The holiday data is currently available for $( wc -l /tmp/sorted | awk '{print $1}' ) countries.
+          
+          > ⚠️ Note that depending on the country, the data might not yet be complete or correct, as the legislature will update their holiday calendar in the next months.
+          
+          See [here](https://github.com/GothenburgBitFactory/holidata) on how you can contribute to updating/adding more locales!
+          
+          If you spot an error, please report it [here](https://github.com/GothenburgBitFactory/holidata/issues/new?labels=bug&template=bug_report.md&title=Error+in+locale+LOCALE%5B%2C+year+YEAR%5D).
+          
+          EOF
+        continue-on-error: false
+
+      - name: Create Pull Request
+        id: cpr
+        uses: peter-evans/create-pull-request@v6
+        with:
+          delete-branch: true
+          commit-message: |
+            Added locale files for year ${{ steps.get-next-year.outputs.year }}
+            
+            Added locale files for year ${{ steps.get-next-year.outputs.year }} of countries ${{ steps.upgrade-year.outputs.countries }}.
+          author: "Holidata Bot <[email protected]>"
+          title: Added locale files for year ${{ steps.get-next-year.outputs.year }}
+          body: |
+            Added locale files for year ${{ steps.get-next-year.outputs.year }} of countries ${{ steps.upgrade-year.outputs.countries }}.
+
+            Auto-generated by [create-pull-request][1]
+
+            [1]: https://github.com/peter-evans/create-pull-request
+          branch: upgrade-year
+
+      - name: Merge Pull Request
+        if: "${{ steps.cpr.outputs.pull-request-number != '' }}"
+        uses: juliangruber/merge-pull-request-action@v1
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          number: ${{ steps.cpr.outputs.pull-request-number }}
+          method: rebase
+
+  build:
+    runs-on: ubuntu-latest
+    needs: upgrade-year
+    environment: github-pages
+    concurrency:
+      group: "pages"
+      cancel-in-progress: false
+    steps:
+      - name: Install Hugo CLI
+        run: |
+          echo "Installing Hugo v${{ vars.HUGO_VERSION }}"
+          wget -O ${{ runner.temp }}/hugo.deb https://github.com/gohugoio/hugo/releases/download/v${{ vars.HUGO_VERSION }}/hugo_extended_${{ vars.HUGO_VERSION }}_linux-amd64.deb \
+          && sudo dpkg -i ${{ runner.temp }}/hugo.deb
+
+      - name: Install Dart Sass
+        run: sudo snap install dart-sass
+
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: "main"
+          submodules: recursive
+
+      - name: Setup Pages
+        id: pages
+        uses: actions/configure-pages@v5
+
+      - name: Install Node.js dependencies
+        run: "[[ -f package-lock.json || -f npm-shrinkwrap.json ]] && npm ci || true"
+
+      - name: Build with Hugo
+        env:
+          # For maximum backward compatibility with Hugo modules
+          HUGO_ENVIRONMENT: production
+          HUGO_ENV: production
+        run: |
+          hugo \
+            --minify \
+            --baseURL "${{ steps.pages.outputs.base_url }}/"
+
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: ./html
+
+  deploy:
+    runs-on: ubuntu-latest
+    needs: build
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
+    concurrency:
+      group: "pages"
+      cancel-in-progress: false
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4