Email addon

### Description

As a user I want to purchase an add on service that will allow me to send notification emails from my flows without having to configure my own mail service.

I want the node to be available in the palette pre-configured with a sender that aligns with my app name eg if I'm example.flowforge.cloud I want to send from example@flowforge.cloud

I don't want to have to configure my own SMTP details, DNS or have a domain to do this.