Redirect from epic details page to work items

Based on discussion: &13514 (comment 1898529321) we need to redirect from /epics/:iid to /work_items/:iid as part of the epic to work item migration.

For testing purpose, it can be valuable to add a parameter to the not trigger the redirect. e.g. force_legacy_epic_view=true. This would make it easier to compare data between legacy epic and a work item. We could allow this only for team members.