feat(referrers): push manifest with subject

[pat-pan]

What this PR does / why we need it

The PR is to implement the feature to push manifest with subject as per the OCI distribution spec v1.1.0.

Which issue(s) this PR resolves / fixes

Resolves / Fixes #159

Please check the following list

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

Attention: Patch coverage is 93.90244% with 10 lines in your changes missing coverage. Please review.

Project coverage is 83.25%. Comparing base (336cd2c) to head (aa8f4a0).

Files with missing lines	Patch %	Lines
.../OrasProject.Oras/Registry/Remote/ManifestStore.cs	87.50%	3 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
+ Coverage   81.70%   83.25%   +1.55%     
==========================================
  Files          35       37       +2     
  Lines        1104     1266     +162     
  Branches      127      149      +22     
==========================================
+ Hits          902     1054     +152     
- Misses        146      149       +3     
- Partials       56       63       +7     

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[pat-pan]

hey @shizhMSFT , just check in with you to see if you have any comment on this PR.

[Wwwsylvia]

LGTM