gt user restack-date

Configure how committer date is handled by restack internal rebases


--use-author-datePasses `--committer-date-is-author-date` to the internal git rebase for restack operations. Instead of using the current time as the committer date, use the author date of the commit being rebased as the committer date. To return to default behavior, pass in `--no-use-author-date`