Suppress long running SignalR connections

[rajkumar-rangaraj]

• SignalR team has added a new Activity Tag http.long_running: true to the Activity to indicate that the request is long running. Ref: Add long running activity tag for SignalR connections dotnet/aspnetcore#32084

Changes

If http.long_running is set to true in Activity.Tag, avoid creating a Request telemetry.

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.

[cijothomas]

changelog entry as well.