Add support for the authn MFE

[arbrandes]

Upstream has implemented a fix to the branding issue. This might make it in as well!

• [x] https://github.com/openedx/frontend-app-authn/pull/681
• [x] https://github.com/openedx/frontend-app-authn/issues/692
• [x] https://github.com/overhangio/tutor-mfe/pull/94

[arbrandes]

We hit a brick wall for Olive: it seems the authentication API used by the Authn MFE requires edx-enterprise to be deployed.

Let's try again in Palm.

[arbrandes]

Turns out the presumed dependency was a red herring. We're good to include authn again, if we want to! I tested it, and it works.

[regisb]

It would be great if we could include all the new MFEs in the olive branch of the plugin, such that we leave some time for testers to at least have a look at the new MFEs. It's not much, but better than nothing.

[arbrandes]

@regisb, I've been rebasing tutor-mfe@olive on nightly, testing, then force-pushing as each is added, so that should be covered a few minutes after the nightly one is merged.

[arbrandes]

Aaaad we're in!