Add Outbox Pattern

[ardalis]

Link to my forthcoming article on sending emails with Outbox.

Also link my ardalis.com article to the deviq outbox pattern description.

[sadukie]

• Ardalis.com - Building a Resilient Email Sending Method in .NET with SmtpClient, Retry Support, and the Outbox Pattern
• Send Email in dotnet with Mimekit, Retry, and Outbox Pattern

[sadukie]

@KyleMcMaster Saw your comment on #455 - heads up that Outbox doesn't have a page either. Let me know the timing of your post, and we can make sure these DevIQ updates get done to work with your post!