feat: add event-based response state

[francescovallone]

As a developer I want to access the current state of the response inside the Middleware to execute code after the execution of the handler if needed.

The InternalResponse class should expose a on method that will require the event to subscribe and the listener function.

The events can be:

• beforeSend. Event triggered before the response has sent the data
• data. Event triggered when the data has been sent.
• afterSend. Event triggered when the data has been sent but the response has not been closed.
• close. Event triggered when the response and the connection has been closed.
• redirect. Event triggered when the handler is redirecting to a new path.
• error. Event triggered when an error has been thrown.
• all. Wildcard for all the events.

The listener should accept a parameter that is the event which triggered it.

The stream should be broadcast to ensure that more listener can listen to the same event.

[francescovallone]

This feature can be used to init the implementation of a sort of Trace API inside Serinus.