Skip Azure VM resource detection on App Service

[Andreas Lillje (alillje)]

Fixes #3179.

Changes

• Skip Azure VM resource detection when the WEBSITE_SITE_NAME environment variable identifies the application as running on Azure App Service.
• Prevent the VM resource detector from making an unnecessary request to the Azure Instance Metadata Service.
• Add a regression test verifying that VM metadata is not requested when running on App Service.

Checklist

• I ran Unit Tests locally.
• CHANGELOG.md updated with one line description of the fix, and a link to the original issue if available.

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[Andreas Lillje (alillje)]

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Pull request overview

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[xiang17]

Since this file is vendored from open-telemetry/opentelemetry-dotnet-contrib (link to this file), it's better to make the corresponding change in the upstream repository and sync it here.

Otherwise it could cause the behavior to diverge from the source project and be overwritten during a future vendor refresh. Ideally, the upstream implementation should become the source of truth, followed by a vendored update here.

[Andreas Lillje (alillje)]

Thanks for the guidance. I’ve now submitted the change upstream: open-telemetry/opentelemetry-dotnet-contrib#5167. I’ll keep this PR as a draft while the upstream change is reviewed.

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