add api to take upstream registry offline

[stonezdj]

fixes #22569

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Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

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• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
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• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.86%. Comparing base (c8c11b4) to head (9e5ad0a).
⚠️ Report is 612 commits behind head on main.

Files with missing lines	Patch %	Lines
src/server/v2.0/handler/project_metadata.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #22696       +/-   ##
===========================================
+ Coverage   45.36%   65.86%   +20.49%     
===========================================
  Files         244     1073      +829     
  Lines       13333   116126   +102793     
  Branches     2719     2931      +212     
===========================================
+ Hits         6049    76486    +70437     
- Misses       6983    35399    +28416     
- Partials      301     4241     +3940     

Flag	Coverage Δ
unittests	65.86% <62.50%> (+20.49%)	⬆️

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Files with missing lines	Coverage Δ
src/pkg/project/models/project.go	39.62% <100.00%> (ø)
src/server/middleware/repoproxy/proxy.go	9.89% <100.00%> (ø)
src/server/v2.0/handler/project_metadata.go	13.60% <0.00%> (ø)

... and 984 files with indirect coverage changes

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