Include Unsubscribe & "View in browser" links for email templates

[chrisbbreuer]

Clear and concise description of the problem

zero config unsubscribing & "viewing in browser" experience.

Suggested solution

• [ ] create "Unsubscribe" feature
• [ ] create "View in browser" feature

Alternative

No response

Additional context

No response

Validations

• [X] Follow our Code of Conduct
• [X] Read the Contributing Guide
• [X] Check that there isn't already an issue that requests the same feature (to avoid creating a duplicate)