[Infra] Wait for NuGet packages to be published during release process

[martincostello]

Changes

This is more of an RFC for now before I'd refactor more of the release process to leverage this fully.

In 2024 I wrote a .NET global tool that waits until one or more NuGet package has been fully published to NuGet.org for release automation. The UX is something like this.

I thought it would be a good idea to use it here to smooth out the release process.

At the moment, the PR to update the versions (e.g. #7125) is opened ~immediately after the release is published from a PR comment (e.g. #7123).

This PR then fails, and needs to be manually re-run once all the relevant packages are indexed and downloadable from NuGet.org.

Instead, if we waited for the NuGet packages to be available and then opened the PR, we'd waste CI resource on doomed-to-fail builds.

For now to illustrate the idea, this PR adds a workflow that waits for all the NuGet packages associated with a release to be published to NuGet.org and then posts a comment on the release PR once they are.

If people are happy, I can do further refactoring to change the workflow to:

• publish release
• post comment that the packages were uploaded
• wait for packages to be published (which can fail and at worst case just introduce a fixed delay)
• open the PR
• post the "done" comment

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.11%. Comparing base (9b45df9) to head (15dda86).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7163      +/-   ##
==========================================
+ Coverage   89.08%   89.11%   +0.03%     
==========================================
  Files         271      271              
  Lines       13073    13073              
==========================================
+ Hits        11646    11650       +4     
+ Misses       1427     1423       -4     

Flag	Coverage Δ
unittests-Project-Experimental	88.97% <ø> (-0.07%)	⬇️
unittests-Project-Stable	89.06% <ø> (+0.07%)	⬆️
unittests-Solution	89.02% <ø> (-0.01%)	⬇️
unittests-UnstableCoreLibraries-Experimental	40.80% <ø> (ø)

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see 3 files with indirect coverage changes