Send a notification mail to the users added to the "credit others" field

Problem/Motivation

I've got credited with the new contribution_records system active yesterday for the following issue https://new.drupal.org/contribution-record/11419456 . in the old system, in cases like that, you would have received a notification email, but with the new system the crediting went completely unnoticed. I wouldn't have noticed that i got credited if i havent read about the issue and that credits were provided for that meeting in a conversation over in the drupal slack.

Steps to reproduce

Proposed resolution

at the moment the only way to notice that you are being credit for an issue you haven't commented on or provided any input is solely that you noticed the addition of a new credit on your user profile page https://www.drupal.org/u/rkoller → but otherwise that information can easily be missed.
i've always appreciated being kept in the loop in the old system and being informed by a notification mail in cases like this. therefore i would suggest to handle it the same way in the new system?

Remaining tasks

User interface changes

API changes

Data model changes