feat(emails): Add `createEmail` to email sending endpoints (#199) r=vladikoff
feat(emails): Add `createEmail` to email sending endpoints (#199) r=vladikoff

This PR adds rate-limiting to all endpoints that send emails for the add secondary email feature. It is a one liner because we reuse the verify code and resend code endpoints in add secondary emails. The only other endpoint that sends an email is the create email operation.

Fixes #180
mozilla/fxa-customs-server,mozilla/fxa-customs-server