Parallel building AMD64 and ARM64 images on appropriate build agents for the arch

[lietu]

Updated dibber after significant reworking on how it accomplishes the goals. Tested on https://github.com/lietu/docker-images

• AMD64 and ARM64 images are built in separate jobs, on separate agents, with the right host type
• Images built on the jobs are uploaded to GHCR based on their digest, and a unique ID for the build
• If both builds succeed, we create manifests with the target tag names including both platform digests, making multi-arch images
• Also uploading output for docker builds for better debugging of slow builds etc.

For details on changes to dibber https://github.com/lietu/dibber/compare/1.0.7..1.1.11

[lietu]

from https://github.com/lietu/docker-images/actions/runs/18978646924