Provide payload with Order ID in EmbeddedCheckoutCompleteEvent

[joshuaballoch]

Is your feature request related to a problem? Please describe.
I run an embedded checkout on a merchant website, where we redirect users to a custom confirmation page (hosted elsewhere), after the users completes their sign up.

I would like to be able to show the user their order ID on this page, but I can't put it in the redirect URL, because I don't have that data.

Describe the solution you'd like
It would be great if the EmbeddedCheckoutCompleteEvent provided the ID of the newly generated order, when the customer checks out.