Provide the ability to get the notification object in PublishCore

I’ve developed a Polly based custom Mediator implementation, in order to add exponential retries and fallback. Therefore, it never throws an exception to the Publish caller.

The overriden PublishCore is clean and simple :

protected override async Task PublishCore(IEnumerable<Func<Task>> allHandlers)
        {
            var tasks = allHandlers.Select(t => _policy.ExecuteAsync(t));
            await Task.WhenAll(tasks).ConfigureAwait(false);
        }

The Polly policy is defined in the constructor, but it could also be injected.

When my Fallback policy triggers, I would like to send the failed notification to an Azure Service Bus Queue, so I can monitor it and replay it later through an Azure Function for example.

In order to achieve that, I would need to get access to the underlying INotification object in the PublishCore method. I see two possibilities:

• Inject a IEnumerable<Expression<Func<Task>>> instead of a IEnumerable<Func<Task>>. Thanks to reflection, I would get access to the INotification object.
• Introduce a breaking change by updating the PublishCore signature in order to provide an INotification notification parameter, even though it wouldn’t be used in the default implementation.

If you’re ok with the idea, I can send a PR based on the preferred solution.

[jbogard]

And I’m open to a PR on this one

[jbogard]

Fixed by #431