Support google/ko attachments (sbom, signatures)

[DennisDenuto]

Describe the problem/challenge you have

google/ko produces sbom's when building an image. However kbld is hardcoded to publish images to the local docker daemon (via --local). Due to the docker daemon unable to store non-container manifests (such as sboms and signatures) these artifacts are dropped when using kbld with ko.

Describe the solution you'd like

Preserve attachment images such as sboms and signatures when using the google/ko builder

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