feat(docker): support per-platform artifact downloads

[nikzen]

Add artifact_per_platform input that, when true, appends the
platform name to the artifact name (e.g. server-amd64, server-arm64).
This allows callers to upload architecture-specific build artifacts
instead of a single shared one. Defaults to false for backward
compatibility.

[github-actions]

* ebd35072ac0966772eea5c03ea1c6b3fc914732c feat(docker): support per-platform artifact downloads
|   - Error: Bad signature: Malformed MPI: leading bit is not set: expected bit 8 to be set in  1001001 (49)
* 57b383862ba81dfa265bb33d492e2bbcbc96891d Revert "chore(docker): use clean_registry in step `Create manifest list and push`"
    - Trust root.

Failed to authenticate commits.

Error: Could not verify commits 57b383862ba81dfa265bb33d492e2bbcbc96891d..ebd35072ac0966772eea5c03ea1c6b3fc914732c

Caused by:
    0: While verifying commit ebd35072ac0966772eea5c03ea1c6b3fc914732c
    1: Bad signature: Malformed MPI: leading bit is not set: expected bit 8 to be set in  1001001 (49)

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