novu: [NV-438] - Add payload content to notification object

Why?

After triggering an event and passing a payload object to it, the payload object is never saved on the message entity returned by the notifications API specifically for the notification center usecase.

What?

Persist the payload object inside the generated Notification Message for the channel including the original payload object sent by the API Users.

Where?

The unit responsible for creating the notification message is located inside the trigger-event.usecase.ts file inside the @novu/api package.

Done definition

• e2e test for the trigger event asserting the created message to contain the payload object when returned by the API.