Description

Instead of using the --cache-to flag, which requires some gymnastics and doesn't seem to be git pull-able, let's just do a git push and use that for our cached image. It seems to work great in my testing, even getting cache hits for some of the layers but not all when appropriate. This should enable us to use kokoro's prefetching feature too.

Dropping --cache-to also means we don't need to use docker-container or buildx.

Related issue

b/255601283

How has this been tested?

I ran a few similar builds, and got partial cache hits on https://source.cloud.google.com/results/invocations/91180c6c-d031-4ff2-ad09-1df2a731e8f9/targets, and full cache hits on https://source.cloud.google.com/results/invocations/38e87531-adde-46c6-ba2d-a19f4c9dfe3a/targets.

Checklist:

• Unit tests
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• Documentation
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• Minor version bump
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