Add multiplatform build hook

Create buildx context

push from the build hook because it's a multiplatform buildx build

push fails as buildx already pushes

hooks/build

@@ -0,0 +1,3 @@
+#!/bin/bash
+docker buildx create --name multiarch --driver docker-container --use
+docker buildx build --platform linux/arm64,linux/amd64 --build-arg BUILDKIT_MULTI_PLATFORM=1 -f $DOCKERFILE_PATH -t $IMAGE_NAME --push .

hooks/push

@@ -0,0 +1,2 @@
+#!/bin/bash
+echo "Nothing to push at this stage, already pushed as part of the multiplatform build step"