Todo: replace sendgrid-go with Email Service in User service

[h1z3y3]

User service uses package github.com/sendgrid/sendgrid-go to send email. But there is Email Service which can replace sendgrid-go;

https://github.com/micro/services/blob/ff49510a73c48620e6ce4e59f2babf26dd7d7f64/user/domain/domain.go#L81-L98