Add email setting to notify co-authors upon article submission

Currently, Janeway sends a submission acknowledgement email only to the submitting/corresponding author via send_submission_acknowledgement. However, co-authors listed on an article submission also need to be notified that the manuscript has been successfully submitted.

This enhancement would add a new email setting that triggers a "Submission Co-authors Acknowledgement" email to all co-authors (excluding the correspondence author) immediately after article submission.

Proposed Solution

• Add a new email template (e.g., submission_coauthor_acknowledgement)
• When a submission is completed, iterate through co-authors, skip the correspondence author, and send an individualised email to each co-author
• Each email should render the template per co-author so that {{ author.full_name }} resolves to the specific recipient's name
• This should be configurable via journal settings (enable/disable)
  Similar work has been done by @gamboz in the WJS Profile Project (sissamedialab/wjs-profile-project) which includes add_coauthors_submission_email_settings

Additional Context

• This feature would improve co-author experience by providing immediate confirmation of submission status
• Co-authors who do not have Janeway accounts (external co-authors) should also be considered for notification if they have valid email addresses in their author records

Why I see this as a good feature Janeway needs:
Unfortunately, there is a growing problem of submissions with fake identities and authors added as co‑authors without their knowledge. That is a whole lot of trouble for a journal if such a submission is published. With this feature and guidelines for authors that all co‑authors must have institutional emails added, those problems can be greatly prevented from happening.