docker: Add GH actions build workflow (#970)

.github/workflows/docker-build.yaml

@@ -0,0 +1,59 @@
+name: Docker Build
+
+on:
+  push:
+    branches:
+      - "master"
+    tags:
+      - "*"
+  pull_request:
+
+env:
+  build_platforms: ${{ vars.BUILD_PLATFORMS || 'linux/amd64,linux/arm64/v8' }}
+  build_image: ${{ vars.BUILD_IMAGE || 'ghcr.io/isso-comments/isso' }}
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v4
+        with:
+          flavor: |
+            latest=false
+          images: ${{ env.build_image }}
+          tags: |
+            type=ref,event=pr
+            type=semver,pattern={{major}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{version}}
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - name: Login to Github Container Registry
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v4
+        with:
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          platforms: ${{ env.build_platforms }}
+
+      - name: Image digest
+        run: echo ${{ steps.docker_build.outputs.digest }}