Tagging cold start impacted requests

[RohitRanjanMS]

Issue describing the changes in this PR

resolves #11543

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information

[Copilot]

Pull request overview

This PR implements tagging for cold start impacted requests by introducing OpenTelemetry activity tracking during host specialization. The changes move cold start tagging from the request execution phase to the host initialization phase, providing better observability for concurrent requests affected by cold starts.

Key Changes:

• Introduces ActivityExtensions class with methods to create and tag specialization activities
• Updates StandbyManager to create and tag activities during host specialization
• Removes previous cold start tagging logic from FunctionExecutionFeature

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/WebJobs.Script/Diagnostics/OpenTelemetry/ActivityExtensions.cs	New extension methods for creating specialization activities and tagging cold starts
src/WebJobs.Script.WebHost/Standby/StandbyManager.cs	Tags activities during specialization with cold start information
src/WebJobs.Script/Diagnostics/OpenTelemetry/OpenTelemetryConstants.cs	Adds constants for new activity source name and specialization operation
src/WebJobs.Script/Diagnostics/OpenTelemetry/ResourceSemanticConventions.cs	Adds constant for cold start impacted tag
src/WebJobs.Script/ScriptHostBuilderExtensions.cs	Updates activity source registration to use WebJobs-specific constants
src/WebJobs.Script/Diagnostics/OpenTelemetry/OpenTelemetryConfigurationExtensions.cs	Adds new activity source to tracing configuration
src/WebJobs.Script.WebHost/Features/FunctionExecutionFeature.cs	Removes old cold start activity tagging
test/WebJobs.Script.Tests/StandbyManagerTests.cs	Adds comprehensive tests for specialization activity creation and tagging
release_notes.md	Documents the new feature