[capz] Automate image building/publishing

[CecileRobertMichon]

• implement CLI for image-builder with Azure (see AWS CLI implementation https://github.com/kubernetes-sigs/image-builder/pull/76)
• Create a (devops?) pipeline to the build images with CI, using the CLI from previous step, similar to the AKS VHD pipeline. Consider checking in the pipeline yaml definition in either the capz or image-builder repo (I think image-builder is probably more appropriate)
• Integrate the pipeline with https://github.com/devigned/pub to automate publishing as an optional step of the pipeline