Add build bench workflow

.github/workflows/build_bench.yml

@@ -0,0 +1,44 @@
+name: Build Bench
+
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - build/bench/**
+      - docker-bake.hcl
+
+  schedule:
+    # Every day at 12:00 pm
+    - cron: 0 0 * * *
+
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Build and test
+        uses: docker/bake-action@v1.6.0
+        with:
+          targets: bench-test
+
+      - name: Login
+        if: ${{ github.repository == 'frappe/frappe_docker' && github.event_name != 'pull_request' }}
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Push
+        if: ${{ github.repository == 'frappe/frappe_docker' && github.event_name != 'pull_request' }}
+        uses: docker/bake-action@v1.6.0
+        with:
+          targets: bench
+          push: true