Switch from local.edly.io to local.openedx.io

[regisb]

Is your feature request related to a problem? Please describe.

As @kdmccormick mentioned here, Axim now provides the local.openedx.io domain name for use within Tutor. We should make the switch to that new domain name before Sumac.

As we learned during the switch from local.overhang.io to local.edly.io, the transition is actually very simple. It's mostly a matter of updating the documentation and telling users about the change.