Change author of cherry-picked commits

Overview

This MR changes the author of cherry-picked commits:

When User A cherry picks a commit authored by User B

Before:

Author: User B
Committer: User A

Now:

Author: User A
Committer: User B

When commit signing with committer email/name enabled:

Author: User A Committer: GitLab

When GitLab Rails implements appending Co-authored-by trailer:

Author: User A
Committer: GitLab

Co-authored-by: User B