feat(referrers): support referrers API

[pat-pan]

What this PR does / why we need it

The PR is to implement the referrers API as per the OCI distribution spec v1.1.0.

Which issue(s) this PR resolves / fixes

Resolves / Fixes #161

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 90.40000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 84.41%. Comparing base (fab26f8) to head (28d3be2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/OrasProject.Oras/Registry/Remote/Repository.cs	87.87%	7 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
+ Coverage   83.79%   84.41%   +0.61%     
==========================================
  Files          38       39       +1     
  Lines        1370     1482     +112     
  Branches      165      185      +20     
==========================================
+ Hits         1148     1251     +103     
- Misses        155      160       +5     
- Partials       67       71       +4     

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[Wwwsylvia]

LGTM with suggestions

[Wwwsylvia]

LGTM

[shizhMSFT]

LGTM