Make it easier to get endpoints within `WithUrls` callback

[afscrome]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

In the WithUrls callback, you probably want access to endpoints on the resource, however ctx.Resource is typed as IResource not IResourceWithEndpoints so you've got to go through a bit of casting, or go through `TryGetEndpoints' a bit awkward to get

.WithUrls(ctx =>
{
   var endpoint = ((IResourceWithEndpoints)ctx.Resource).GetEndpoint("http");
   //or
   if(ctx.Resource.TryGetEndpoints(out var endpoints))
   {
      var endpoint2 = endpoints.Single(x => x.Name == "http");
   }

   ctx.Urls.Add(new ResourceUrlAnnotation {
      Url = $"{endpoint.Url}/swagger",
      DisplayText = "swagger",
      Endpoint = endpoint
   });
})

Describe the solution you'd like

It would be nice if there was an easier way to get an endpoint in this callback, perhaps

.WithUrls(ctx =>
{
   var endpoint = ctx.GetEndpoint("http");
   // ...
})

Additional context

cc @DamianEdwards

[DamianEdwards]

URLs can be added to any resource, not just those with endpoints, so that's why it's typed as IResource. We could consider adding a helper method to the context but I'm not sure it's worth it? How common do you think it will be to need to grab an endpoint from inside the callback?

[afscrome]

Yea, I get why the type has to be IResource.

How common do you think it will be to need to grab an endpoint from inside the callback?

I assumed that the vast majority of urls would want to use an endpoint in one form or another, although maybe #8638 and #8636 help reduce the need to break into the callback form overall.

[DamianEdwards]

Closed in #8743