Add Refund Event for Refund Creation

[vjung28]

Is your feature request related to a problem? Please describe.
Right now we have a RefundStateTransitionEvent which only gets published when the State of a Refund gets transitioned (As the name suggests).
In our case we need to react on a Refund when it gets created, so in state pending.
As the state was transitioned, we can't listen to an event for that case.

Describe the solution you'd like
Having a RefundEvent with the type "created" would be great.