CI: Push Docker images for pull requests and main

[losolio]

Enables automated Docker image publishing after successful integration tests, supporting multi-environment Kubernetes workflows:

• Production: Pin to versioned releases (manual tagging)
• Staging: Use :canary tag - automatically updated on every r4/master push

[Copilot]

Pull request overview

This PR enables automated Docker image publishing to DockerHub after successful integration tests, supporting a multi-environment deployment strategy. Images are tagged differently based on the trigger: :canary for pushes to r4/master (staging), and :edge-<sha> for pull requests (development/preview environments). External fork PRs are excluded from publishing for security.

Changes:

• Migrated from simple docker build commands to GitHub Actions' build-push-action with multi-architecture support (amd64, arm64)
• Added automated Docker image pushing after successful tests with environment-specific tagging
• Implemented PR commenting to inform developers of the published image tags for testing

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[kennethmyhra]

I like the canary build, we can drop the edge build for now

[kennethmyhra]

We can swap this one out with the one from our secrets secrets.DOCKERHUB_ORGANIZATION. See

spark/.github/workflows/docker_image_linux.yml

Lines 42 to 45 in 0c2903f

	${{ secrets.DOCKERHUB_ORGANIZATION }}/spark:${{ steps.vars.outputs.tag }}
	${{ secrets.DOCKERHUB_ORGANIZATION }}/spark:r4-latest
	${{ secrets.DOCKERHUB_ORGANIZATION_2 }}/spark:${{ steps.vars.outputs.tag }}
	${{ secrets.DOCKERHUB_ORGANIZATION_2 }}/spark:r4-latest

[losolio]

Closing this for now. Should be rethought later.