Added workflow for PR previews

.github/workflows/preview.yml

@@ -0,0 +1,84 @@
+name: Deploy PR previews
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - closed
+
+concurrency: preview-${{ github.head_ref }}
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build-preview:
+    if: github.event_name == 'pull_request_target' && github.event.action != 'closed'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Use Node.js
+        uses: actions/setup-node@1a4442cacd436585916779262731d5b162bc6ec7 # v3.8.2
+        with:
+          node-version: '18'
+      - name: Checkout
+        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Build
+        run: |
+          npm install
+          npm run build
+      - name: Upload artifact
+        uses: actions/upload-artifact@a8a3f3ad30e3422c9c7b888a15615d19a852ae32 # v3.1.3
+        with:
+          name: 'site'
+          path: ./public
+
+  deploy-preview:
+    needs: build-preview
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    environment:
+      name: pull-request-preview
+      url: ${{ steps.deployment.outputs.deployment-url }}
+    steps:
+      # checkout required for pr-preview-action to succeed,
+      # while the content will not be used
+      - name: Checkout
+        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+      - name: Download the preview page
+        uses: actions/download-artifact@9bc31d5ccc31df68ecc42ccf4149144866c47d8a # v3.0.2
+        with:
+          name: 'site'
+          path: ./public
+      - uses: rossjrw/pr-preview-action@4668d7cb417ce7067b0b59bc152b1ae1513010de # v1.4.6
+        id: deployment
+        with:
+          source-dir: ./public
+          preview-branch: previews
+          umbrella-dir: pr-previews
+          deploy-repository: eclipse-sprotty/sprotty-previews
+          token: ${{ secrets.DEPLOY_PREVIEW_TOKEN }}
+          action: auto
+
+  # remove the preview page when the PR got closed
+  remove-preview:
+    if: github.event_name == 'pull_request_target' && github.event.action == 'closed'
+    runs-on: ubuntu-latest
+    steps:
+      # checkout required for pr-preview-action to succeed,
+      # while the content will not be used
+      - name: Checkout
+        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+      - uses: rossjrw/pr-preview-action@4668d7cb417ce7067b0b59bc152b1ae1513010de # v1.4.6
+        id: deployment
+        with:
+          preview-branch: previews
+          umbrella-dir: pr-previews
+          deploy-repository: eclipse-sprotty/sprotty-previews
+          token: ${{ secrets.DEPLOY_PREVIEW_TOKEN }}
+          action: auto