Include pipeline run link in generated azure-sdk-for-net upgrade PR

[Copilot]

PRs auto-created by the C# emitter publish pipeline in azure-sdk-for-net (e.g. Azure/azure-sdk-for-net#59504) had no link back to the Azure DevOps pipeline run that produced them, making traceability painful.

Changes

• packages/http-client-csharp/eng/scripts/Submit-AzureSdkForNetPr.ps1 — added an optional -PipelineRunUrl parameter. When supplied, it renders as an extra bullet under the existing Details section using the same $(if (...) { @"..."@ }) pattern already used for the optional regen sections; when omitted (e.g. local runs) the PR body is unchanged.
• packages/http-client-csharp/eng/pipeline/publish.yml — composed the URL from built-in ADO variables (System.CollectionUri / System.TeamProject / Build.BuildId) to match the shape from the issue (https://dev.azure.com/azure-sdk/<project>/_build/results?buildId=<id>&view=results), exposed it as $(PipelineRunUrl), and passed it through to the script.

Resulting PR body excerpt

## Details

- TypeSpec commit that triggered this PR: https://github.com/microsoft/typespec/commit/<sha>
- Pipeline run that produced this PR: https://dev.azure.com/azure-sdk/internal/_build/results?buildId=<id>&view=results

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-csharp@10829

commit: 49fb1b9