Create E2E email testing infrastructure with email reporting test

[benbowler]

Feature Description

For Email Reporting, we should add E2E tests that actually test sending real email using MailPit, RE this comment.

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Acceptance criteria

• E2E infrastructure should be able to send email, and all emails should be caught by MailPit.
• Each Email Reporting template variant should have an E2E test case added, which validates sending as well as email content and structure.

Implementation Brief

Test Coverage

QA Brief

Changelog entry