Provide means for accepted session authors to confirm they will present

Problem/Motivation

Move the work to implement a solution for session authors to confirm or decline their accepted sessions here, since it will be more technically complex.

This will include:

• Allow speakers to transition their sessions from Accepted to Confirmed
• Explore including a solution like Content Moderation Link so that speakers can confirm their session with a single click from their notification email

Proposed resolution

Potentially implement Content Moderation Link in confirmation email to provide a "one click" solution. Also, consider implementing a block/link that would show for session authors to perform the same operations on the session page.

Implementing the email links might be easier once #3506030: Incorporate the Easy Email: Express Mail recipe is implemented.