Enhance EmailSendEvent with Metadata

[Anddrrew]

Is your feature request related to a problem? Please describe.
In version 2.2, the EmailSendEvent was introduced, which triggers when an email is successfully sent or fails to send. However, as of version 2.2.4, this event is difficult to handle because it comes with rather general fields. It would be beneficial to have a way to identify the email from its creation, through the handler, and during the processing of the EmailSendEvent.

Describe the solution you'd like
Add a metadata field that allows us to attach important data so we can identify the email for further processing.

Additional context
The discussion on Discord: Link

[michaelbromley]

@Anddrrew would you be interested in attempting to implement this feature?

[Anddrrew]

@michaelbromley Yes, I would try. But a little later, sometime after the 17th.