v9: Added Extension method to register all custom Notifications

[mclausen]

Description

Let me ask you a question. How many tears have you felt, running down your chin, every-time you’d forgot to register your freshly created notification? How many times do you think you’d started the cms, and didn’t add your notifications? If you are like me, that is more than once, and that is too many.

What if i told you that you’d never had to forget to registers any custom notification handlers ever again, and that the solution would be helpful and friendly at the same time?

Enter this PR.

What does it do? It is an immediate pain reliever, that comes in a form of an Extension Method to IUmbracoBuilder named AddNotificationsFromAssembly<T> where T is the type within the assembly your or the customer custom notifications is located. It locates all your implementations of INotificationHandler<TNotification> and registers them in the IServiceCollector so you dont have to manually remember and add them your self.

How does it look in the wild?

You can add all notifications on One line

public class MyFavoriteComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.AddNotificationsFromAssembly<Startup>();
    }
}

Whatever custom notification that you have in your project will now be registered and the best thing is, that if you create a new one, then you no longer have to forget to register it.

Cheers 🍻

[Zeegaan]

Found a few very minor things, rest of the code LGTM 👍

Tested this and it works great, never forgetting to register a notification again!
Will be happy to merge once the changes are made 💪

[mclausen]

Thank you for the feedback @Zeegaan 🙌

[Zeegaan]

With the minor changes i am now happy to merge, great work 💪