[Enhancement] Add extensions methods to dynamically add and subscribe to integration event handlers

[Erik Hakobyan]

Now
builder.Services.AddTransient<ProductPriceChangedIntegrationEventHandler>();
builder.Services.AddTransient<OrderStatusChangedToShippedIntegrationEventHandler>();
builder.Services.AddTransient<OrderStatusChangedToPaidIntegrationEventHandler>();

var eventBus = app.Services.GetRequiredService<IEventBus>();
eventBus.Subscribe<ProductPriceChangedIntegrationEvent, ProductPriceChangedIntegrationEventHandler>();
eventBus.Subscribe<OrderStatusChangedToShippedIntegrationEvent, OrderStatusChangedToShippedIntegrationEventHandler>();
eventBus.Subscribe<OrderStatusChangedToPaidIntegrationEvent, OrderStatusChangedToPaidIntegrationEventHandler>();

After
builder.Services.AddIntegrationEventHandlers(Assembly.GetExecutingAssembly());

app.SubscribeIntegrationEventHandlers(Assembly.GetExecutingAssembly());

I have already implemented and tested this functionality, which works fine and removes unnecessary lines of code from the startup.