Rename region tags in aspnetcore sample.
Rename region tags in aspnetcore sample.

Corresponding doc is https://cloud.google.com/trace/docs/setup/aspnetcore.

GoogleCloudPlatform/dotnet-docs-samples,GoogleCloudPlatform/dotnet-docs-samples,GoogleCloudPlatform/dotnet-docs-samples,GoogleCloudPlatform/dotnet-docs-samples