Add manifestcache push for tag and digest to local repository

[raphaelzoellner]

Comprehensive Summary of your change

Harbor Proxies will push a manifest referencing a digest and tag to the local repo if both are known.

Issue being fixed

Fixes #21122

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• [x] Well Written Title and Summary of the PR
• [ ] Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• [x] Accepted the DCO. Commits without the DCO will delay acceptance.
• [x] Made sure tests are passing and test coverage is added if needed.
• [x] Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[stonezdj]

Thanks for your contribution! because the current code change doesn't fix the issue #21122, and might result in regression issue, so we will close this PR.

[raphaelzoellner]

Hello @stonezdj,

could you give a hint why this code change (creating the manifest referenced by the tag) wouldn't solve or at least improve the described behavior in #21122, so one can think about another solution?

Is this maybe a misunderstanding with the PR https://github.com/goharbor/harbor/pull/21123, which is already closed?