no issue
- refactored `renderEmailPreview` into separate fetch and render functions
- grab email info from an existing email resource if it exists on the post rather than fetching a preview
- added "View email" button the the email-sent state of the newsletter settings PSM section
no issue
- changed `disabled=deliveredAction` to `disabled=mailgunError` so that it's switching on the correct property
- removed all references to the unused `deliveredAction` property
no issue
- removed unnecessary scratch value handling for a non-model property
- use [`oneWay`](https://api.emberjs.com/ember/release/functions/@ember%2Fobject%2Fcomputed/oneWay) to bind the logged in user's email address to the `testEmailAddress` property on the component - this allows for the default value to always be the logged in users email but changing the property value only changes the value on the component, not upstream on the user model
- use default two-way binding of the `<Input>` helper to avoid unnecessary boilerplate
- removed unnecessary usage of the `truncate` helper for the placeholder
