CodePipeline cd-container-images pipeline

[denizgenc]

Not sure if this is ready to leave draft yet (the ECR module is still sourced from a development branch, instead of the main branch, so I guess it depends on alphagov/cyber-security-shared-terraform-modules#6), but it has demonstrated that:

• Auto-update of the pipeline works
  • Though it should be noted that if the pipeline has a new stage added to it, every stage following the auto-update stage is paused and needs to be kicked off manually
• Both the Docker Hub and ECR modules can build the concourse-base-image (here called cyber-security-cd-base-image) and push them to their respective registries

[alice-carr]

The ECR branch has now been merged to master, so marking this as ready to review