Adds eleventy build action

Author: SaptakS

.github/workflows/gh-pages.yml renamed to .github/workflows/eleventy_build.yml

@@ -6,6 +6,11 @@ jobs:
     runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@main
+      - name: Build
+        uses: TartanLlama/[email protected]
+        with:
+          args: --pathprefix='/foss.training/'
+          install_dependencies: true
       - name: Deploy
         uses: peaceiris/actions-gh-pages@v3
         with: