Add copilot-setup-steps.yml

[ericstj]

This will enable us to use Copilot agent in this repo.

Test results -- https://github.com/dotnet/machinelearning/actions/runs/15594105366

[Copilot]

Pull Request Overview

This PR adds a new GitHub workflow that sets up the environment for the Copilot agent in the repository.

• Introduces a workflow triggered manually via the Actions tab.
• Configures the job to check out code, install dependencies, build the project, and adjust the .NET path.

[tarekgh]

LGTM!

[ericstj]

Helix is down.
RestApiException1: The response contained an invalid status code 500 Internal Server Error `

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.99%. Comparing base (aea5651) to head (505d2e6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7481      +/-   ##
==========================================
- Coverage   68.99%   68.99%   -0.01%     
==========================================
  Files        1482     1482              
  Lines      273880   273880              
  Branches    28254    28254              
==========================================
- Hits       188956   188955       -1     
+ Misses      77540    77539       -1     
- Partials     7384     7386       +2     

Flag	Coverage Δ
Debug	68.99% <ø> (-0.01%)	⬇️
production	63.28% <ø> (-0.01%)	⬇️
test	89.45% <ø> (ø)

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see 6 files with indirect coverage changes

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