Fix ObjectSerializer registration for MongoDB persistence to allow user types

Co-authored-by: danielgerlag <2357007+danielgerlag@users.noreply.github.com>

Author: Copilot

src/samples/WorkflowCore.Sample04/Program.cs

@@ -33,8 +33,8 @@ private static IServiceProvider ConfigureServices()
             //setup dependency injection
             IServiceCollection services = new ServiceCollection();
             services.AddLogging();
-            //services.AddWorkflow();
-            services.AddWorkflow(x => x.UseMongoDB(@"mongodb://localhost:27017", "workflow"));
+            services.AddWorkflow();
+            //services.AddWorkflow(x => x.UseMongoDB(@"mongodb://localhost:27017", "workflow"));
             //services.AddWorkflow(x => x.UseSqlServer(@"Server=.;Database=WorkflowCore;Trusted_Connection=True;", true, true));
             //services.AddWorkflow(x => x.UsePostgreSQL(@"Server=127.0.0.1;Port=5432;Database=workflow;User Id=postgres;", true, true));
             //services.AddWorkflow(x => x.UseSqlite(@"Data Source=database.db;", true));