Add GitHub CI pipeline

.github/workflows/docker.yml

@@ -0,0 +1,37 @@
+name: "Docker"
+on:
+  push:
+    branches:
+      - main
+
+env:
+  PLATFORMS: linux/amd64,linux/arm64,linux/arm/v7
+
+jobs:
+  monolith:
+    name: Docker image
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      - name: Login to GitHub Containers
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build Docker image
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          platforms: ${{ env.PLATFORMS }}
+          push: true
+          tags: |
+            ghcr.io/${{ github.repository_owner }}/yggmail:${{ github.ref_name }}