chore(): set up preview build

.github/workflows/preview.yml

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+# This is a basic workflow to help you get started with Actions
+
+name: CI
+
+# Controls when the workflow will run
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  push:
+    branches: [ dev ]
+  pull_request:
+    branches: [ dev ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: Setup Node.js environment
+        uses: actions/[email protected]
+
+      - name: Replace tokens
+        # You may pin to the exact commit or the version.
+        # uses: cschleiden/replace-tokens@4f7e3d67f3ff2317ae650842145cdbaefba65189
+        uses: cschleiden/[email protected]
+        with:
+          files: '["**/usage-analytics.ts"]'
+        env: 
+          ANALYTICS_CODE: ${{secrets.ANALYTICS_CODE}}
+
+      - name: Build
+        run: |
+          npm install
+          npx vsce package --out preview.vsix
+          
+      - name: Upload
+        uses: actions/upload-artifact@v2
+        with:
+          name: vsix-package
+          path: preview.vsix
+