Fix: throw a more meaningful error message if Saga Id is not set

[AlexZeitler]

This code

public class Order : Saga
{
  public string? Id { get; set; }

  public object[] Start(
    OrderPlaced orderPlaced
  ) => [new BillOrder(orderPlaced.OrderId)];

  ...
}

leads to this error message currently:

Envelope Envelope #0192bea2-f2a8-4536-9ffb-9a2ecc2ab466/CorrelationId=908b7494-c052-43a0-88e5-0494374ff2bb (Messages.OrderPlaced) from Sales to rabbitmq://queue/placedorders-shipping was moved to the error queue
      System.InvalidOperationException: Type Shipping.Order does not have a public Id property
         at Wolverine.Persistence.Sagas.InMemorySagaPersistor.Store[T](T document) in /home/runner/work/wolverine/wolverine/src/Wolverine/Persistence/Sagas/InMemorySagaPersistor.cs:line 37
         at Internal.Generated.WolverineHandlers.OrderPlacedHandler1858006213.HandleAsync(MessageContext context, CancellationToken cancellation)
         at Wolverine.Runtime.Handlers.Executor.ExecuteAsync(MessageContext context, CancellationToken cancellation) in /home/runner/work/wolverine/wolverine/src/Wolverine/Runtime/Handlers/Executor.cs:line 164

New text will be:

Type Shipping.Order Id property must be set to a non-null value.