upstream: Add proxy cache hit/miss metrics (goharbor/harbor#23578)

[github-actions]

Summary

Cherry-picks upstream Harbor commit f7c9eda10 from goharbor/harbor#23578.

Upstream Context

• Upstream PR: Add proxy cache hit/miss metrics goharbor/harbor#23578
• Upstream commit: f7c9eda10ddb8a8289b5bc758bd8f31fd5594e93
• Upstream title: Add proxy cache hit/miss metrics
• Upstream author: @Jason-Lee3
• Upstream merged by: @chlins
• Upstream approved by: @chlins, @stonezdj
• Upstream PR URL: Add proxy cache hit/miss metrics goharbor/harbor#23578
• Upstream commit URL: goharbor/harbor@f7c9eda

Cherry-Pick Status

• Status: clean
• Base branch: main
• Workflow run: https://github.com/container-registry/harbor-next/actions/runs/30790785287

Upstream Description

Comprehensive Summary of your change

Added http_registry_proxy_requests_total and http_registry_proxy_upstream_requests_total metrics to monitor proxy cache hit/miss ratio.

Issue being fixed

Fixes goharbor/harbor#22799

Please indicate you've done the following:

• 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"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

Review Notes

• Generated by the upstream cherry-pick workflow.
• One upstream commit maps to one Harbor Next PR.
• If this PR is closed without merge, the workflow will not recreate it.

Upstream-Commit: f7c9eda10ddb8a8289b5bc758bd8f31fd5594e93
Upstream-PR: goharbor/harbor#23578
Cherry-Pick-Status: clean