nightly builds hopefully (#681)

Co-authored-by: Fabian Posenau <fabian@fphome.de>

.github/workflows/build_docker_v2.yml

@@ -44,7 +44,8 @@ jobs:
     - name: Docker Setup Buildx
       uses: docker/setup-buildx-action@v2.5.0
 
-    - name: Build and push Docker images
+    - name: Build and push stable release
+      if: github.event.release.prerelease == false
       uses: docker/build-push-action@v4.0.0
       with:
         context: .
@@ -54,3 +55,14 @@ jobs:
         push: true
         tags: ${{ secrets.DOCKERHUB_USERNAME }}/ontime:${{ env.RELEASE_VERSION  }} , ${{ secrets.DOCKERHUB_USERNAME }}/ontime:latest
 
+    - name: Build and push pre-release
+      if: github.event.release.prerelease == true
+      uses: docker/build-push-action@v4.0.0
+      with:
+        context: .
+        file: ./Dockerfile
+        platforms: linux/amd64,linux/arm64,linux/arm/v7,linux/arm/v6
+        # Push is a shorthand for --output=type=registry
+        push: true
+        tags: ${{ secrets.DOCKERHUB_USERNAME }}/ontime:${{ env.RELEASE_VERSION  }} , ${{ secrets.DOCKERHUB_USERNAME }}/ontime:nightly
+