Use bereq object for managing implicit redirects in MIT Learn

[blarghmatey]

In the MIT Learn application, if someone hits the http -> https redirect the first time it leaks the path rewriting that is done for managing the React routing state. This results in a 404 and bad UX

Expected Behavior

The user cleanly redirects from http -> https without getting a 404

Current Behavior

The user gets a 404 because of trying to load /frontend/index.html

Steps to Reproduce

1. In a clean session go to http://learn.mit.edu

Possible Solution

Move the path rewriting to a fetch stage snippet and manipulate the bereq.url instead of req.url