refactor(api): split startup configuration

Tiku.Api/Configuration/ApiPresentationExtensions.cs

@@ -0,0 +1,23 @@
+using System.Text.Json.Serialization;
+using Tiku.Api.OpenApi;
+
+namespace Tiku.Api.Configuration;
+
+internal static class ApiPresentationExtensions
+{
+    internal static IServiceCollection AddApiPresentation(this IServiceCollection services)
+    {
+        services.AddControllers()
+            .AddJsonOptions(options =>
+            {
+                options.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
+            });
+        services.AddOpenApi(options =>
+        {
+            options.AddDocumentTransformer<BearerSecuritySchemeTransformer>();
+        });
+        services.AddProblemDetails();
+
+        return services;
+    }
+}