docker build workflow

- automatically creates a multi-arch Docker image upon merging PRs to main

.github/workflows/main.yml

@@ -0,0 +1,47 @@
+name: Build and Push Docker image
+
+on:
+  pull_request:
+    types: [closed]
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.merged == true
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+        with:
+          version: latest
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: hummingbot/dashboard:latest
+          platforms: linux/amd64,linux/arm64
+          build-args: |
+            BRANCH=${{ github.ref }}
+            COMMIT=${{ github.sha }}
+            BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')
+          cache-from: type=registry,ref=hummingbot/dashboard:latest
+          cache-to: type=inline
+
+      - name: Image digest
+        run: echo ${{ steps.docker_build.outputs.digest }}