test: PoC publish via artifact-gateway with dd-pkg

[AliDatadog]

Summary

PoC to validate dd-pkg publish-image as a replacement for direct public-images trigger blocks.

Replaces publish_public_main trigger block with a script: job using the dd-pkg Docker image (registry.ddbuild.io/agent-delivery/dd-pkg).

Safe test values:

• Source: actual pipeline-built operator image
• Destination: operator-dev:gateway-poc-${CI_PIPELINE_ID} (throwaway)
• Registry: registry.datad0g.com only (staging)
• Manual trigger

Related

• RFC: https://datadoghq.atlassian.net/wiki/spaces/BARX/pages/6342213931
• dd-pkg PR: https://github.com/DataDog/dd-pkg/pull/126
• dd-source PR: https://github.com/DataDog/dd-source/pull/395205
• BARX-1709

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.98%. Comparing base (a1206ff) to head (c97bc49).
⚠️ Report is 36 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2883      +/-   ##
==========================================
+ Coverage   38.94%   42.98%   +4.03%     
==========================================
  Files         313      319       +6     
  Lines       27139    31356    +4217     
==========================================
+ Hits        10570    13479    +2909     
- Misses      15780    16955    +1175     
- Partials      789      922     +133     

Flag	Coverage Δ
unittests	42.98% <ø> (+4.03%)	⬆️

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see 71 files with indirect coverage changes

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