Replaces `build-push-action` buildx QEMU building for multiple `arch` with a multi-runner matrix that builds each image on native runners and combines digests before pushing to registries.
* Use arm public preview runner
* Refactor publish image workflow to use multi-runner
* Refactor PR workflow to use multi-runner
* All required files in the same file by using .actrc
* Include example .secrets and .env
* Update README with usage
* Refactor actTest to make docker build steps optional with ENV
* Aligns with "normal" default branch usage better, allows dependabot to actually run
* Change image publishing to push tagged images as 'latest' and master images as `edge`