add fork preview deployment workflow

.github/workflows/deploy_docs_preview_forks.yml

@@ -0,0 +1,23 @@
+name: Deploy
+
+on:
+  pull_request_target:
+
+permissions:
+  checks: write
+  contents: read
+  deployments: write
+  pages: write
+  id-token: write
+
+jobs:
+  deploy:
+    if: ${{ github.repository != github.event.pull_request.head.repo.full_name }}
+    name: Preview
+    # SHA for security hardening. Points at last verified HEAD of main branch.
+    uses: primer/.github/.github/workflows/deploy_preview.yml@cd223835608ca5e9401e0ffe6081f6d2fcc912f3
+    with:
+      node_version: 16
+      install: npm ci --legacy-peer-deps && cd apps/docs && npm ci --legacy-peer-deps && cd ..
+      build: npm run build && npm run build:docs:preview && npm run build:storybook:preview
+      output_dir: apps/docs/public/