[FEATURE] Support co-authors

[BSFishy]

Is your feature request related to a problem?
It would be nice for backports to recognize the original author(s) of the pull-request. At this point in time, backports say that the commit was authored by the Github Actions bot. I think if a commit in the original PR has a co-author, the backport will get that author as well, however the main author is never recognized.

What solution would you like?
The action should extract a list of (co-)authors from the commits of the original PR and craft a list of co-authors to place in the backport commit.

What alternatives have you considered?
I haven't looked into it, but it might be possible to author the commits using the original author's name/email. I don't know how well that would fit into this action, or if it is actually possible.

Do you have any additional context?
In OUI, our release workflow generates a changelog based on the commit diff between the previous release and current release: https://github.com/opensearch-project/oui/releases/tag/1.3.0 The issue is that the original PR authors don't get recognized in the release, as (almost) all of the PRs are backported, thus the original author is lost.

https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors

[VachaShah]

@BSFishy Thank you for raising this issue!

The commit in the backport PR already shows the original author (its shows the original author and Github Actions bot both as the author):

The backport pull requests are then created by the opensearch-trigger-bot which is the Github App.

The "by opensearch-trigger-bot" that you see in the release notes is picked by Github when you auto-generate the release notes since it takes the name of the user that creates the pull requests. Unfortunately, there is no way for the pull request to be created by the original user as it is an automated workflow so it has to be created by a Github App.

[BSFishy]

That doesn't seem right to me, based on what I am seeing in my repo. For that PR that you mentioned, I was actually the original author of the PR:

@seanneumann would be considered a co-author in that case, if I'm not mistaken, which is probably why he got carried through but I didn't. For PRs that only have a primary author and no co-authors, no additional users come up:

Perhaps I have the workflow set up incorrectly? But I also don't see anything in this repo to do anything with the original PR's author. Not sure, I think it would be very cool to have the original author list without the bot as well.

If I'm not mistaken, you can author a commit as one user and push/raise a PR with another (which is why GPG signing is a thing). Basically meaning the commit is authored by the original user but the PR is authored by the bot