Build Frontend workflow (stanford-crfm/helm)

# Build the frontend from source, and open a pull request to commit the build artifacts.
# This allows Python users to use the React frontend without installing and running Node.
name: Build Frontend
 
on:
  push:
    branches:
      - 'main'
    paths:
      - 'helm-frontend/**'
      - '.github/workflows/build-frontend.yml'
 
concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true
 
jobs:
  build:
    timeout-minutes: 30
    runs-on: latchkey-small
    steps:
    - name: Checkout code
      uses: actions/checkout@v4
    - name: Use Node.js
      uses: actions/setup-node@v4
      with:
        cache: 'npm'
        node-version: '18'
    - name: Install Yarn
      working-directory: ./helm-frontend
      run: npm install --global yarn
    - name: Install dependencies
      working-directory: ./helm-frontend
      run: yarn install
    - name: Build app
      working-directory: ./helm-frontend
      run: yarn build --outDir '../src/helm/benchmark/static_build' --emptyOutDir
    - name: Write README.md
      run: echo -e '# Frontend Build\n\nThis directory is automatically generated by GitHub Actions and contains a static site built from helm-frontend. Do not modify this directory!' > src/helm/benchmark/static_build/README.md
    - name: Git add
      run: git add --force src/helm/benchmark/static_build
    - name: Create pull request
      uses: peter-evans/create-pull-request@v6
      with:
        commit-message: Build frontend
        branch: actions/build-frontend
        delete-branch: true
        title: 'Build frontend'
        body: Auto-generated from GitHub Actions.