Added custom mvc setup method to testserver base class (#16545)

Author: lars-erik

tests/Umbraco.Tests.Integration/TestServerTest/UmbracoTestServerTestBase.cs

@@ -278,6 +278,8 @@ protected void ConfigureServices(IServiceCollection services)
 
                     // Adds Umbraco.Tests.Integration
                     mvcBuilder.AddApplicationPart(typeof(UmbracoTestServerTestBase).Assembly);
+
+                    CustomMvcSetup(mvcBuilder);
                 })
                 .AddWebServer()
                 .AddWebsite()
@@ -294,6 +296,11 @@ protected void ConfigureServices(IServiceCollection services)
             builder.Build();
         }
 
+        protected virtual void CustomMvcSetup(IMvcBuilder mvcBuilder)
+        {
+            
+        }
+
         /// <summary>
         ///  Hook for registering test doubles.
         /// </summary>