fixes https://github.com/TryGhost/Team/issues/2368
- Removed the usage of the `isLocalContentImage` Koenig util for the
email header and feature image url generation.
- While we were trying to set the width to 1200px, we didn't have that
size hardcoded. So that url would redirect back to the original location
instead of serving a smaller image. So I added a new internal size to
the `imageOptimization` config.
- This is fixed in both the new and old email flow and includes some
extra tests for the new flow.
closes https://github.com/TryGhost/Team/issues/2309
- adds new mailgun provider to send out batch emails
- updates sending service to send email id for mailgun provider, allows tagging mail with email id
fixes https://github.com/TryGhost/Team/issues/2308
- Still has some missing pieces, but mostly works.
- Uses new handlebars template for emails
- When sending emails with the new email stability flag enabled, one
test email is now sent via the default smtp ghost mailer.
fixes https://github.com/TryGhost/Team/issues/2284
New batch sending flow (still WIP). Logs the sent emails instead of actually sending them. Unit tests are coming in later commits.
