ft: adds GH option to ignore cache upload failures

[urimandujano]

We've seen a lot of failures attempting to upload our built images to the GithubActions Cache API. This PR updates our build and upload step to ignore failures resulting from cache uploads. This should let the CI continue without using cached images. The idea here is its better for the CI run to continue without a cached image than it is to crash if we can't cache anymore.

Reference PRs:

• New feature - feat: allow ignoring remote cache-export error if failing moby/buildkit#3430

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[chrisguidry]

That's good thinking!

[urimandujano]

I'm going to go ahead and merge this because:

• the failure in the workflow is related to a recurring flake "Alarm based timeouts can only be used in the main thread." which is being tracked here
• it looks like the option to ignore cache upload failures is working in this PR because we hit the timeout and the workflow was able to proceed + succeed. This should help our ongoing flake work:

exporting to GitHub Actions Cache
preparing build cache for export
preparing build cache for export 305.2s done
ERROR: maximum timeout reached
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