Revert issue description in issue/mr/epic to older version
Follow up to https://gitlab.com/gitlab-org/gitlab-ee/issues/10103.
In #10103 (closed), you can view changes to a description, but you cannot go back to a previous version. This can be problematic especially if there is a big change and you don't want to copy and paste. This feature allows a user to revert an older version.
We may want to take this approach or just use Git instead. See https://gitlab.com/gitlab-org/gitlab-ee/issues/10849.