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 90.34091% with 17 lines in your changes missing coverage. Please review.

Project coverage is 82.86%. Comparing base (a9103d2) to head (7df36ca).

Files with missing lines	Patch %	Lines
.../OrasProject.Oras/Registry/Remote/ManifestStore.cs	86.48%	3 Missing and 7 partials ⚠️
src/OrasProject.Oras/Registry/Remote/Referrers.cs	89.09%	4 Missing and 2 partials ⚠️
src/OrasProject.Oras/Registry/Remote/Repository.cs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #163      +/-   ##
==========================================
+ Coverage   81.70%   82.86%   +1.16%     
==========================================
  Files          35       37       +2     
  Lines        1104     1278     +174     
  Branches      127      152      +25     
==========================================
+ Hits          902     1059     +157     
- Misses        146      154       +8     
- Partials       56       65       +9     

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