Add latest tag to Docker build explicitly (close #61)

Author: istreeter

.github/workflows/test.yml

@@ -71,17 +71,27 @@ jobs:
         DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
     - name: Stage the Docker build
       run: sbt "project loader" docker:stage
+    - name: Docker metadata
+      id: meta
+      uses: docker/metadata-action@v3
+      with:
+        images: snowplow/snowplow-postgres-loader
+        tags: |
+          type=raw,value=latest,enable=${{ !contains(steps.ver.outputs.tag, 'rc') }}
+          type=raw,value=${{ steps.ver.outputs.tag }}
+        flavor: |
+          latest=false
     - name: Set up QEMU
       uses: docker/setup-qemu-action@v1
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v1
-    - name: Build image
+    - name: Push image
       uses: docker/build-push-action@v2
       with:
         context: modules/loader/target/docker/stage
         file: modules/loader/target/docker/stage/Dockerfile
         platforms: linux/amd64,linux/arm64/v8
-        tags: snowplow/snowplow-postgres-loader:${{ steps.ver.outputs.tag }}
+        tags: ${{ steps.meta.outputs.tags }}
         push: true
 
   deploy_common: