Add Enrich to OnCustom in HttpInListener

[Tornhoof]

Feature Request

All the main HttpInListener methods call the Enrich functor to add additional data to the activity, e.g. OnStartActivity, OnStopActivity, OnException. Only OnCustom does not.
I suggest adding to:

opentelemetry-dotnet/src/OpenTelemetry.Instrumentation.AspNetCore/Implementation/HttpInListener.cs

Lines 244 to 264 in 13e721d

	public override void OnCustom(string name, Activity activity, object payload)
	{
	if (name == "Microsoft.AspNetCore.Mvc.BeforeAction")
	{
	if (activity.IsAllDataRequested)
	{
	// See https://github.com/aspnet/Mvc/blob/2414db256f32a047770326d14d8b0e2afd49ba49/src/Microsoft.AspNetCore.Mvc.Core/MvcCoreDiagnosticSourceExtensions.cs#L36-L44
	// Reflection accessing: ActionDescriptor.AttributeRouteInfo.Template
	// The reason to use reflection is to avoid a reference on MVC package.
	// This package can be used with non-MVC apps and this logic simply wouldn't run.
	// Taking reference on MVC will increase size of deployment for non-MVC apps.
	_ = this.beforeActionActionDescriptorFetcher.TryFetch(payload, out var actionDescriptor);
	_ = this.beforeActionAttributeRouteInfoFetcher.TryFetch(actionDescriptor, out var attributeRouteInfo);
	_ = this.beforeActionTemplateFetcher.TryFetch(attributeRouteInfo, out var template);
	if (!string.IsNullOrEmpty(template))
	{
	// override the span name that was previously set to the path part of URL.
	activity.DisplayName = template;
	activity.SetTag(SemanticConventions.AttributeHttpRoute, template);
	}

try
{
    this.options.Enrich?.Invoke(activity, "OnCustom", payload);
}
catch (Exception ex)
{
    AspNetCoreInstrumentationEventSource.Log.EnrichmentException(ex);
}

This would allow adding more data from the payload, including additional information from the Action, e.g. other attributes or different routeData information.
Example: I use an extended version of the routing attributes to match incoming routes based on extra headers, similar to the concepts described in 5 levels of Hypermedia and the extra information would be useful as tag data.

[vishweshbankwar]

PR removes this event subscription: #5026