Improve endpoint route template detection for minimal APIs

[stevejgordon]

When using the APM agent with ASP.NET Core minimal APIs, the transaction will default to using the path in the name, which can lead to high-cardinality transaction names and difficulty analysing them in the APM UI. This is because the current APM code expects to look for controller or page routing information, which is not present for minimal APIs.

We should enhance WebRequestTransactionCreator.StopTransaction to extract a more relevant transaction name for minimal API requests.

As a workaround, the new transaction_name_groups feature will support a way to manually group transactions for minimal APIs.