cache docker build layers

* testing if gha cache is used



https://docs.docker.com/engine/reference/commandline/buildx_build/#cache-from

https://docs.docker.com/engine/reference/commandline/buildx_build/#cache-to

* try out inline cache



src: https://github.com/moby/buildkit#export-cache

* go back to using gha cache

.github/workflows/build-images.yml

@@ -72,3 +72,5 @@ jobs:
           push: true
           tags: ${{ vars.DOCKERHUB_TAG }}:${{ steps.image_tag.outputs.TAG }}
           platforms: linux/amd64,linux/arm64,linux/arm/v7
+          cache-from: type=gha
+          cache-to: type=gha,mode=max