Add custom email destination and more to broadcast emails for archiving

Problem/Motivation

Thanks for the suggestion to open a new issue, @john.oltman, and for your great ongoing work! Perhaps I'm not the only one who would appreciate an additional field for a configurable default email address to which a copy of the mail to the recipient group gets sent for later reference and archiving.

Such an administrative extra mail could perhaps show some abbreviated form of the event's name (entered manually together with the admin mail recipient?), and the recipients' group's status and "Sent" date and time in the title, perhaps in brackets, e.g., like the Mailman list software headers, before the title of the mail.

The body could display the list of recipients' mail addresses, preferably together with their names if available, and/or the user names on the system if they are registered users of this Drupal installation, or "anonymous" or "guest" if they aren't, plus of course the content that got sent in the body.

Names may be useful when one want's to check whether some people received information that was sent only to a subset of the registrants and you cannot reconstruct quickly whether these people were on the waitlist or already had completed their registration at the time - and it may be quicker to find that out when you have a chance to see a name beside "happy12345 @ gmail.com" among the listed recipients.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes