Providing Sample Projects

[tsutomi]

This PR comes with three new sample projects, and some fixes to the design of the libraries, discovered during the runtime of the projects:

• ASP.NET Core Notification Application - Manages subscriptions to webhooks, receives event notifications, constructs webhooks and delivers them to the subscribers
• ASP.NET Core Receiver Application - Receives webhooks through a route in a pipeline and through a MVC API controller
• ASP.NET Core Receiver (Mininal API) - A minimal API application that receives webhooks to a path
• Lifetime of the Webhook Subscription management adjusted to 'Scoped', to align the scope of the multi-tenant resolution