Redirect legacy iteration routes

When :iteration_cadences FF is enabled, the legacy iteration routes should be redirected to their corresponding iteration cadence routes. An iteration is now a sub-resource of a cadence and new urls reflect the change like in http://gdk.test:3000/groups/my-group/-/cadences/8026/iterations/66/edit.

Legacy routes:

• http://gdk.test:3000/groups/my-group/-/iterations
• http://gdk.test:3000/groups/my-group/-/iterations/new
• http://gdk.test:3000/groups/my-group/-/iterations/show
• http://gdk.test:3000/groups/my-group/-/iterations/edit