support OCI-Subject header

[wy65701436]

the response header OCI-Subject to indicate to the client that the registry processed the request's subject.

Thank you for contributing to Harbor!

Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

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.

[codecov]

Codecov Report

Merging #18885 (701012f) into main (1d2624e) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main   #18885      +/-   ##
==========================================
+ Coverage   67.37%   67.39%   +0.01%     
==========================================
  Files         981      981              
  Lines      107193   107194       +1     
  Branches     2698     2698              
==========================================
+ Hits        72224    72243      +19     
+ Misses      31088    31066      -22     
- Partials     3881     3885       +4     

Flag	Coverage Δ
unittests	67.39% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/server/middleware/subject/subject.go	51.78% <100.00%> (+0.87%)	⬆️

... and 6 files with indirect coverage changes

[chlins]

lgtm