v5.12.2 add platform injection support

Changes

• Add/platform override support (#5) @rl-io

Upgrading

To upgrade, update your pipeline.yml files:

steps:
  - command: test.sh
    plugins:
-     docker-compose#v5.12.1:
+     docker-compose#v5.12.2:
        image: someimage
        workdir: /app

5.12.1 with 3pl customisations

Contains changes in the upstream 5.12.1 release, but includes the changes for builder options to push-on-build

This allows buildx to create and push multi-arch images which was previously not possible