Simplify adding co-authors when merging PRs

Description

I occasionally feel like adding co-authors to people who helped to write a PR, however this is a multi-step process and sometimes I forget.

I wish there was a way to simplify tagging authors and automatically generating the correct Co-authored-by: line.

GitHub's docs don't help here, they just mention "go find the email". I have to

1. open the profile
2. open a repo
3. find a commit
4. open the patch
5. copy the "author" line
6. manually type Co-authored-by: making sure I don't misspell it

I think this could be sped up by either:

• adding a "Copy co-authored-by line" button on the profile
• adding a "Collect co-authors" button, which generates a line for all visible users on the PR

The first one would be generic and also work for commits created anywhere (🤷‍♂️) while the second one would be more visible and immediately useful when merging.

The problem is getting that email address. I think we could just generate the line using the username and the custom GitHub email. Not perfect but instant and maybe good enough.

Example URLs

• https://github.com/refined-github/sandbox/pull/12