Allow displaying past issues

[picocodes]

Currently, only admins can preview email campaigns. We need to add a way to display past newsletter issues.

Maybe a shortcode?

How will merge tags work if we don't know the current subscriber/customer/user?

[picocodes]

This has been added:- https://noptin.com/guide/sending-emails/how-to-display-past-newsletter-issues-on-your-site/

I will update the shortcode if anyone proposes other enhancements.