add trigger site build

Author: jukent

.github/workflows/trigger-site-build.yaml

@@ -0,0 +1,11 @@
+name: trigger-site-build
+on:
+  pull_request:
+
+jobs:
+  build:
+    uses: ProjectPythia/cookbook-actions/.github/workflows/build-book.yaml@main
+    with:
+      artifact_name: book-zip-${{ github.event.number }}
+      base_url: '/${{ github.event.repository.name }}/_preview/${{ github.event.number }}'
+      # Other input options are possible, see ProjectPythia/cookbook-actions/.github/workflows/build-book.yaml