Use the new CreateSlimBuilder API

The `dotnet new api -aot` template is getting updated to use the new slim API in dotnet/aspnetcore#46040. Updating the benchmark to match.

Author: eerhardt

src/Goldilocks/Program.cs

@@ -1,7 +1,7 @@
 using System.Text.Json.Serialization;
 using Goldilocks;
 
-var builder = WebApplication.CreateBuilder(args);
+var builder = WebApplication.CreateSlimBuilder(args);
 builder.Logging.ClearProviders(); // Clearing for benchmark scenario, template has AddConsole();
 
 builder.Services.ConfigureHttpJsonOptions(options =>
@@ -27,4 +27,4 @@
 internal partial class AppJsonSerializerContext : JsonSerializerContext
 {
 
-}
+}