Add a configuration option for the Co-Authored-By: line

[albertlarsan68]

Hello,

The Co-Authored-By line in the commit message is present to add attribution for the merges as stated in #382, but I have two suggestions:

• There should be an option to disable it, because when the person cited as co-authors activated the vigilant mode on Github, this shows as "partially verified" (orange, and orange is not perfect). Currently, there is no way to mark it as verified (green, and green is better).
• Second, I think the line should be filled not by the PR author, but by the person that r+ed it. This would show correct attribution, since the commits (in the merge workflow) are already attributed to the PR author.

Thanks,