Original code authors get automatically added to MR participants

Description

In a big project with multiple people working on the same features, sometimes its hard to keep an overview how code is evolving over time.

For example a developer different from the original author is fixing a bug. The original author might never notice and therefore doesn't get the chance to learn from his mistakes. Also when a feature is enhanced/modified the original author may have something to say about the matter.

Proposal

In a merge request, whenever a code line is deleted or modified the original author is added to the list of the merge request participants and gets informed via email.

~"feature proposal"