feat: add optional BuildKit cache-from/cache-to inputs

[DeepDiver1975]

Summary

• Adds two optional inputs docker-cache-from and docker-cache-to to the docker-build reusable workflow
• Both inputs are wired into the docker/build-push-action build step (cache-from+cache-to) and the publish step (cache-from only — no write on publish)
• Defaults to empty string, so all existing callers are unaffected

Test plan

• Verify existing callers (ubuntu images) still build without setting the new inputs
• Verify a caller passing type=gha / type=gha,mode=max gets BuildKit layer cache hits on re-runs

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