fixes https://github.com/TryGhost/Team/issues/2346
- Adds email batch browse endpoint
- Adds email recipient failures browse endpoint
- Adds new fixtures and E2E tests for the new API
- Added support for snapshot tests to have 'nullable' types.
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.
refs https://github.com/TryGhost/Toolbox/issues/354
- this commit turns the Ghost repo into a monorepo so we can bring our
internal packages back in, which makes life easier when working on
Ghost
