E&M: Support for order refund events

[krzysztofwolski]

### Tasks
- [ ] Add subscription for ORDER_REFUNDED
- [ ] Add add example template and payload
- [ ] Make ORDER_REFUNDED available for Saleor versions >= 3.14
- [ ] Add subscription for ORDER_FULLY_REFUNDED
- [ ] Add add example template and payload
- [ ] Make ORDER_FULLY_REFUNDED available for Saleor versions >= 3.14

[lkostrowski]

@krzysztofwolski can we close this?

[krzysztofwolski]

Closing, functionality has been implemented. Both partial and full refund are triggering an email.