Re-add the old EdXOpenIdConnect backend temporarily.
Re-add the old EdXOpenIdConnect backend temporarily.

This solves a transient issue during rollout where old browser
sessions that were established before rollout would fail to authenticate
with the new ecommerce code because DRF could not find the correct
backend to assign to the request.

New browser sessions will still use the first listed backend, which
is still EdXOAuth2.

edx/ecommerce,edx/ecommerce,eduNEXT/edunext-ecommerce,edx/ecommerce,eduNEXT/edunext-ecommerce,eduNEXT/edunext-ecommerce,eduNEXT/edunext-ecommerce,edx/ecommerce