feat: Add organization artifact metadata APIs

[maishivamhoo123]

Description

This PR implements the Organization Artifact Metadata APIs as requested in #3917.
This version corrects the scope from Repository to Organization level.

Changes

• Logic: Moved implementation to github/orgs_artifacts.go.
• Endpoints Added:
  • POST /orgs/{org}/artifacts/metadata/deployment-record
  • POST /orgs/{org}/artifacts/metadata/deployment-record/cluster/{cluster}
  • POST /orgs/{org}/artifacts/metadata/storage-record
  • GET /orgs/{org}/artifacts/{subject_digest}/metadata/deployment-records
  • GET /orgs/{org}/artifacts/{subject_digest}/metadata/storage-records
• Testing: Added comprehensive unit tests in github/orgs_artifacts_test.go.
• Generated: Updated github-accessors.go and github-stringify_test.go via script/generate.sh.

Checklist

• I have reviewed my own diff for unnecessary changes.
• All tests pass (script/test.sh).
• Code is linted (script/lint.sh).
• Ran script/generate.sh.

Fixes #3917

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.41%. Comparing base (a21a651) to head (39a1ebc).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
github/orgs_artifacts.go	77.77%	5 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3944      +/-   ##
==========================================
- Coverage   92.45%   92.41%   -0.05%     
==========================================
  Files         203      204       +1     
  Lines       14980    15025      +45     
==========================================
+ Hits        13850    13885      +35     
- Misses        927      932       +5     
- Partials      203      208       +5     

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[maishivamhoo123]

@gmlewis Sir can you please review the code?

[gmlewis]

Thank you, @maishivamhoo123, @alexandear , and @Not-Dhananjay-Mishra!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @zyfy29

[maishivamhoo123]

@Not-Dhananjay-Mishra can you please check once i think the latest pr is able to meet all your requirements?

[alexandear]

@maishivamhoo123 this comment is not addressed: https://github.com/google/go-github/pull/3944/changes#r2732556939

Should be a separate struct for the request body.